Load Bearing Structural Elements of Glulam in Marine Environment

Load Bearing Structural Elements of

Glulam in Marine Environment

A literature and case study

Bärande konstruktionselement av limträ i marin miljö En litteratur- och fallstudie

Karin Abrahamsson

Faculty of Health, Science and Technology Degree Project for Master of Science, Mechanical Engineering 30 hp Supervisor: Lasse Jacobsson Examiner: Jens Bergström 2020-07-05

Abstract

This thesis discusses the possibilities of using glued laminated timber as load bearing structural elements in structures in close vicinity of saltwater. Glued laminated timber, also referred to as glulam, is a refined timber product constructed of timber lamellae that are glued together. The thesis contains a literature study and a case study that covers glulam beams in a pedestrian jetty located on the Swedish west coast. The literature study addresses wood in relation to moisture, the effects that salt may have on wood in a marine environment, wood decaying mechanisms and suitable wood preservatives to prevent decay. The literature study also covers glulam as a material and the possibilities of wood pressure impregnation. A method of estimating the service life of timber elements is also discussed.

The results of the literature study were applied in a case study of a specific case, to explore the possibility of replacing the current steel beams of the structure with glulam beams. From the case study, the strength and deflection of the prospective glulam beams were calculated. Service life of the prospective glulam beams was estimated based on the environment they would be exposed to. An analysis of the market for glulam products in Sweden was also performed to find out what dimensions and wood impregnation classes are available.

The results of the literature study show that glulam can be used as main load bearing elements in a marine environment, given that the structure is placed above sea level. Salt water does not affect the wood, rather it works as a wood preservative and gives some protection against rot. However, the structure is subjected to high moisture content and pressure impregnation is necessary. The high moisture content also affects the mechanical properties of the wood as the strength and stiffness of glulam decrease with increasing moisture content. Creep of the material is also affected as it increases with increased moisture content.

Regarding strength and deflection, the results of the case study show that glulam beams available on the Swedish market are of sufficient dimensions to be used. Regarding service life, the case study showed that the estimated service life of the glulam beams is only 19 years, but the service life required is 50 years. The current structure design with prospective glulam beams does not meet the requirements for durability of the material. However, suitable design changes regarding wood moisture protection could increase service life of the glulam beams.

Sammanfattning

Denna rapport behandlar möjligheterna till att använda tryckimpregnerat limträ som huvudbärverk i konstruktioner i nära anslutning till saltvatten. Limträ är en träprodukt bestående av trälameller som limmats samman till större träelement. Rapporten består av en litteraturstudie och en fallstudie som behandlar limträbalkar i en promenadbrygga belägen på den svenska västkusten. Litteraturstudien avhandlar trä i förhållande till fukt, eventuell påverkan av salt i en marin miljö, nedbrytningsmekanismer för trä samt lämpliga träskydd för att förhindra nedbrytning. Litteraturstudien behandlar även limträ som material och möjligheterna till tryckimpregnering. En metod för att uppskatta livslängden av trä diskuteras också.

Resultaten från litteraturstudien applicerades i en fallstudie för ett specifikt fall, för att undersöka möjligheterna att ersätta den nuvarande konstruktionens stålbalkar med limträbalkar. Utifrån fallstudien beräknades hållfastheten och nedböjningen av de tilltänkta limträbalkarna. Livslängden på de tilltänkta limträbalkarna uppskattades baserat på den miljö de skulle komma att utsättas för. En analys av marknaden av tryckimpregnerade limträprodukter i Sverige genomfördes också för att se vilka dimensioner och tryckimpregneringsklasser som finns att tillgå.

Resultatet från litteraturstudien visar att limträ kan användas som huvudbärverk för marina konstruktioner med kravet att konstruktionen placeras ovanför vattenytan. Saltvatten påverkar inte träet negativt utan verkar snarare som träskydd mot röta. Dock utsätts konstruktionen för hög fuktkvot och måste därför tryckimpregneras. Det höga fuktinnehållet påverkar även de mekaniska egenskaperna av träet då hållfastheten och styvheten av limträet minskar med ökande fuktkvot. Krypningen av träet påverkas också, då krypning ökar med ökad fuktkvot.

Med avseende på hållfasthet och nedböjning visade resultatet av fallstudien att tryckimpregnerat limträ som kan erhållas från den svenska marknaden är av tillräckliga dimensioner för att kunna användas. Avseende livslängd visade fallstudien att den undersökta konstruktionens estimerade livslängd endast är 19 år. Dock är den erfordrade livslängden för träkonstruktionen 50 år. Dagens konstruktion möter inte kraven på materialets varaktighet, men längre livslängd skulle kunna erhållas genom lämpliga designändringar avseende limträbalkars skydd mot fukt.

Table of Content

1 INTRODUCTION ...... 1

1.1 BACKGROUND ...... 1

1.2 AIM ...... 3

1.3 QUESTION ...... 3

1.4 GOALS ...... 4

1.5 LIMITATIONS ...... 4

2 METHOD ...... 5

3 LITERATURE STUDY ...... 6

3.1 TIMBER ...... 6

3.2 MOISTURE ...... 8

3.3 DURABILITY ...... 9

3.4 WOOD PRESERVATIVES ...... 11

3.5 GLUED LAMINATED TIMBER ...... 14 3.5.1 Timber structures: European standard SS-EN 14080 ...... 16

3.6 DURABLE DESIGN OF TIMBER STRUCTURES ...... 18 3.6.1 Requirements and regulations ...... 19 3.6.2 Moisture ...... 20 3.6.3 Marine Environment ...... 21 3.6.4 Preservative treatment ...... 22

3.7 SERVICE LIFE ...... 23 3.7.1 Required service life ...... 24 3.7.2 Severity class ...... 24 3.7.3 Exposure conditions ...... 25 3.7.4 Material resistance �� ...... 33

3.8 CASE STUDY ...... 33 3.8.1 Preservative treatment ...... 35 3.8.2 Calculations of strength and deflection ...... 36 3.8.3 Calculation of glulam beam in ULS ...... 38 3.8.4 Calculations of the glulam beam in SLS ...... 39

4 RESULTS ...... 41

4.1 LITERATURE STUDY ...... 41

4.2 ON THE MARKET ...... 42

4.3 CASE STUDY ...... 44 4.3.1 Calculation in ULS ...... 45 4.3.2 Calculations in SLS ...... 46 4.3.3 Service life ...... 48

5 DISCUSSION ...... 50

5.1 LITERATURE STUDY ...... 50

5.2 ON THE MARKET ...... 51

5.3 CASE STUDY ...... 52

6 CONCLUSIONS ...... 55

7 REFERENCES ...... 57

APPENDIX A

1 Introduction

1.1 Background

Large jetties and pedestrian bridges located in marine environments most often use beams made of steel as load bearing structural elements. Steel offers high strength which can handle large spans and due to good protection against corrosion it also provides a long service life. In a marine environment, salt in the seawater causes problems. For steel this is a big concern because a moisture rich and saline environment will induce corrosion. Corrosion of steel can be limited through well-established methods of rustproofing, like for instance galvanization. For surface treatment such as galvanization to maintain its function, machining of the element should not be done after treatment. This leads to high demands on tolerances during production, since machining on the building site is not possible for a long service life. Moreover, steel beams are most often covered with wooden cladding to give a softer architectural expression. Figure 1-3 shows a pedestrian jetty, designed by Ramboll Sweden AB, located in Lysekil on the Swedish west coast. Cladding, decking and handrailing are made of pressure impregnated wood and the load bearing beam is made of galvanized steel. As can be seen, the steel structure is covered to give the impression of a structure made entirely of wood.

Figure 1: Pedestrian jetty in Lysekil, designed by Ramboll Sweden AB, department of Port and Marine Structures.

Figure 2: Pedestrian jetty in Lysekil, designed by Ramboll Sweden AB, department of Port and Marine Structures.

Figure 3: Pedestrian jetty in Lysekil, designed by Ramboll Sweden AB, department of Port and Marine Structures.

Glued laminated timber can be used as load bearing beams as an alternative to steel. Timber as a construction material has generally a lower carbon footprint in comparison to steel. It is also more flexible in the context of machining on the building site and a visible timber

2 structure would not require any extra coverage or cladding from an architectural point of view which would reduce the use of material. It would therefore be beneficial in terms of cost, climate and material usage to use timber as load bearing structure instead of steel. Structures such as jetties and pedestrian bridges presented in Figure 1-3 will be exposed to a moisture rich environment caused by weather and splashing and spraying from the sea. The load bearing timber beams will most often be inaccessible, therefore service in form of continuous painting is not suitable. Instead pressure treatment is preferred. Under these circumstances, will glued laminated timber be an optional material to use? What is the influence of moisture, salt, weather and wood preservatives? And, is it possible to use timber with respect to strength, durability and service life?

1.2 Aim

This project will evaluate the possibility of using glued laminated timber as load bearing structural elements for jetties and pedestrian bridges in a marine environment. The aim is to reduce the climate impact by using timber instead of steel with retained load bearing strength and service life in a coastal environment.

1.3 Question

The question this thesis aims to discuss is whether glued laminated timber can replace steel with regard to strength, durability and service life as the main load bearing elements for large jetties and small bridges in a marine environment.

3 1.4 Goals

The goals with this project are: • To evaluate the possibilities of using strength-classified glulam with pressure impregnation in a marine environment above the waterline. • To theoretically investigate and show the possibilities of the use of timber with respect to strength, durability and service life with the expectation to be used in real projects in the future. • To apply the theoretical findings and perform calculations on one specific case illustrated in Figure 1-3. • To estimate expected service life, with respect to fungal decay of glulam beams in a marine environment, to see if the required lifetime of 50 years is reachable.

1.5 Limitations

• This thesis will only consider structural timber from Scots pine and Norwegian spruce since they are the main construction timber used in Sweden. • The research will be focused on Swedish weather conditions in a coastal environment. • The glulam elements are going to be located above the water line. • Detailing such as fixings and fittings will not be dealt with.

4 2 Method

This project was performed theoretically and was divided into three main parts: a literature study, a case study and an analysis of the existing market of pressure impregnated glulam in Sweden.

The literature study aimed at collecting information necessary to thoroughly evaluate the possibility of using glulam in a marine environment. Information on the following topics was gathered in the literature study: - Timber and the effects of moisture on timber - The influence of salt on timber in a marine environment - Wood decaying mechanisms - Suitable preservative treatment methods to prevent wood decaying mechanisms - Glulam as a material and the possibility of pressure impregnating it - Method of estimating expected service life of timber structure members

The case study was done on the pedestrian jetty presented in the introduction, Figure 1-3. As a complement to the case study, an analysis of the market for pressure impregnated glulam in Sweden was also done. The purpose of the analysis was to see what kind of glulam beams are available on the market and what preservative classifications they have.

The case study evaluated the possibility of replacing current steel beams with pressure impregnated glulam beams. This was done by; - Applying findings from the literature study - Incorporating findings from the analysis of the market of pressure impregnated glulam in Sweden - Performing calculations regarding strength and deflection of the glulam beams - Estimating expected service life of the glulam structure based on the environment it will be subjected to.

Calculations were performed using Wolfram Mathematica.

5 3 Literature study

Timber is one a of the oldest construction materials. It is a cheap and effective material made by nature and it is widely used due to its diversity in different areas of usage. One of the greater abilities of timber is that it is renewable, and compared to other construction materials on the market, timber is the only renewable one. The environmental concerns and awareness of global warming have increased the interest for more sustainable materials like timber. An increased amount of timber used in construction can reduce the amount of other non- renewable construction materials like concrete, steel and brick. These non-renewable materials also require a lot of energy in their primary production and have higher CO2 emission compared to timber [1]. In many constructions, timber can replace other constructive materials and still provide the same functionality. During the last decades, an improvement of timber as a constructive material has happened. For instance, timber bridges made of glulam can have large cross section and span over a range of 5-40m and be designed for the same function and service life as steel and concrete bridges [2].

Compared to steel and concrete, timber is often considered to be less durable and expected to have a much shorter lifetime. Timber used outdoors might be exposed to elevated levels of moisture and show serious decay after just a few years of service, which has led to the perception of a non-durable material. However, structures like Norwegian stave churches and covered bridges in Switzerland are examples of timber designs that show great durability. Knowledge of the material and the surrounding environment, along with good design and detailing, can extend the lifetime of timber structures, making them at least as durable as any other construction material for appropriate application [2].

3.1 Timber

In Sweden, the main timber used in the construction industry comes from Scots pine or Norwegian spruce since these are the most common trees in the area. These species belong in the family of softwood. Softwood is necessarily not softer than hardwood. The wood hardness can vary a lot within both categories, but it is accurate to say that the hardest hardwood is much harder than any softwood. Softwood is mainly made up of so-called heartwood and sapwood. The inner core of the trunk is called the heartwood, and between the bark and the

6 heartwood the sapwood is located. In many softwood species these two can be visually distinguished, because the heartwood has a darker color than the sapwood [3, 4].

Wood is a natural fiber composite built up of three main constituents; cellulose, hemicellulose and lignin. Some other substances are also present, one of them is resin. Wood is mainly made up of long, vertical and hollow cells resembling a bundle of pipes. These cells are referred to as fibers, which due to their hollow structure are able to transport water and nutrition. The cells in the heartwood are blocked and clogged with resin which makes them unable to carry water and therefore have a lower moisture content. The cells in the sapwood are not clogged which makes them able to transport water and have therefore a high moisture content. For water and nutrition transportation in radial direction, there are medullary rays that go from the inner bark and inwards. This macrostructure of the wood trunk can be seen in Figure 4 [5].

Figure 4: Cross section of wood trunk [1].

The aligned fiber structure generates an anisotropic material. Timber is orthotropic, meaning that it has higher stiffness in the fiber direction than perpendicular to the fibers. Timber is stronger in the fiber direction than perpendicular to the fibers regardless of whether the load is caused by tension, compression or bending. It also has greater tensile strength along the fiber

7 direction than in compression due to buckling of the fibers. The material properties can vary within the same timber component and between components of the same species. This is because the strength is affected by many different parameters such as density, defects in the timber, moisture content and temperature. It is therefore of importance to deal with stresses in timber with a high safety margin [1, 5].

Since the strength can vary greatly, timber is sorted in different strength classes for different areas of usage. The sorting process can be done visually or mechanically. Visual grading is important for detecting defects in the timber such as knots, holes, sloping grains, compression wood etc. Timber with smaller and fewer knots are graded into higher classes. The mechanical grading is used for determining the mechanical properties of the timber, such as strength and Young’s modulus. Construction timber needs to be strength-graded according to Swedish standards and are labeled with CE, which guarantees that the product meets the European requirements for health, environment and safety [6].

3.2 Moisture

Timber is hygroscopic, meaning that it will absorb moisture from the atmosphere when the wood is dry and, correspondingly, emit moisture when it is wet. In wood, moisture can exist in three different phases: as bound water, free water and as water vapor. When water enters into the dry timber, the water molecules are first bound to the cellulose in the cell walls. When these are saturated, the cell cavity starts to fill up with free water and water vapor instead. The absorption and transportation of water in the sapwood are mainly done by capillary absorption in the hollow fibers. Some absorption can take place in the end grain of the heartwood but other than that, the closed cells in the heartwood prevent transportation of water. Due to the aligned hollow fiber structure, the absorption is twenty times larger in the fiber direction than in radial direction. It is therefore important to protect the end grain from moisture, since this is where wood most easily absorbs water [3, 5].

The strength and stiffness are dependent of the moisture content. An increased moisture content will increase density and reduce strength and Young’s modulus until the fiber saturation point. The fiber saturation point is defined as the moisture content where the cell wall is filled with bound water molecules, but the cell cavities are still empty. At this point the

8 moisture content does not influence the mechanical properties any longer. For softwood, this appears at around 25-30% moisture. Additional increase of moisture will therefore not affect the mechanical properties further. The moisture content also influences the strength of the material. The strength decreases with increased moisture content until the fiber saturation point is reached. From this point, the strength can be considered constant. In a similar manner, absorption and release of moisture up to the fiber saturation point lead to swelling or shrinkage, which is illustrated in Figure 5. The movement of timber related to swelling or shrinkage, is anisotropic. The largest movement appears in tangential direction, followed by radial direction. Movement in the fiber direction is very small in comparison and can be assumed to be negligible. The moisture content also influences the amount of creep. Creep increases with higher moisture content [3, 5].

(%)

Swelling

Figure 5: Movement of softwood as a function of the moisture content [1].

3.3 Durability

The service life and durability of timber structures are hard to predict. Durability of wood relates to several degrading mechanisms influenced by the surrounding environment, moisture, decay fungi and insects. Different types of wood have different natural resistance to degrading mechanisms. Heartwood, for instance, has good natural protection against wood- decaying mechanisms due to its high content of resin and the closed fiber cells which both prevent the transport of water. On the other hand, sapwood generally has no resistance to wood decaying mechanisms and biological attack. There is also a difference in durability of

9 different wood species because of their ability to absorb and release moisture. For instance, heartwood of Swedish oak is more durable than heartwood of pine or spruce. There is currently no quantitative method to evaluate the deteriorating process, since there are so many parameters that influence the durability of wood. The service life of timber structures is therefore hard to predict, and this is why timber is considered to be less durable in comparison to concrete or steel [1, 7]. However, a recent study made by RISE, has developed an arbitrary method to predict the expected service life of timber bridges with the purpose to give guidelines for construction design of future wooden structures. This will be presented in chapter 3.7 [2].

The most important deterioration mechanism is fungal decay, also referred to as rot. Rot is caused by fungi that grow in the wood, destroying the material by breaking down the cellulose, hemicellulose and lignin. This causes a reduction in strength of the material. The wood-destroying fungi require four conditions for their existence; oxygen, nutrition, suitable temperature and moisture. The nutrition is provided by the timber itself and for the rot fungi to thrive, a surrounding temperature of 0°- 40° should be present. Rot-fungi also require free water, which can be maintained if the moisture content is above the fiber saturation point of 25-30% [1].

There are three main groups of wood-decaying fungi; brown rot, white rot and soft rot. White rot mainly attacks hardwood and can be recognized by a white and fibrous structure. Since it mainly affects hardwood, it is not a big concern in buildings and structures made of softwood. Brown rot, on the other hand, is the most common fungal decay in buildings. Brown rot turns the timber brown with deep cracks running across the grain, which divides the wood into rectangular pieces. Timber affected by brown rot will show a decrease in strength quite instantly after the brown rot has occurred. In environments with high moisture content and a low oxygen level, soft rot can occur. Soft rot is, for instance, often present in timber in contact with the ground or submerged in marine or freshwater environment. An attack by soft rot will erode the surface layer of the timber at a relatively slow rate, giving it a soft and spongy texture. Wet timber can also be attacked by insects, although this can often be a sign that fungal decay is already present in the timber [8, 9].

Timber used in marine environment is subjected to marine-boring animals. These are particularly active in tropical water with a high salt content and can cause severe damage in a

10 short period of time. For Swedish conditions, this problem only concerns the west coast and the marine-boring animal called shipworm. The shipworm primarily attacks the wood in the waterline but can be found up to a depth of 10 meters. For timber used above the water line, shipworm is not a concern [3, 5]. Moreover, a marine environment and more specifically the presence of chlorides causes a harsh environment especially for steel due to corrosion. For timber, saltwater can actually act as a wood preservative. A heavy salt decomposition may offer some protection against fungal decay, provided that the timber member is located above the water line. However, the salt content may vary over time [9, 10].

3.4 Wood preservatives

To protect the timber from biological attack, one of the four factors; temperature, nutrition, oxygen and moisture, needs to be controlled. The easiest to control is moisture content, which should primarily be controlled by structural wood protection, where the timber is mechanically protected from long-term moisture absorption by sheltering and design. In constructions where this is not possible and the material is permanently in contact with moisture, wood preservatives can be used instead. This is a chemical treatment that can be done in various ways, with the main purpose to prevent the rot-fungi to get nutrition from the wood [1].

Wood preservatives are used to increase the lifetime of timber, more specifically, it makes the sapwood more durable. For application of wood preservatives, a variety of methods are available where impregnation is the most effective one. Surface treatment by brushing, spraying, or dipping is less effective in preserving the material due to poor penetration of the preservative. When these methods are used, only the surface layer is penetrated. Scratches or splits that may occur on the surface will expose untreated timber and enable wood-destroying organisms to attack. These methods are therefore most often used as a complement to other impregnation methods [3].

The most effective methods of wood preservatives are industrial methods of timber pressure impregnation. Timber is then sealed in a pressure vessel and vacuum or high pressure is established. Preservative substances are introduced into the vessel which makes the preservative diffuse into the material. Vacuum impregnation and pressure impregnation

11 operate on the premises of a change in applied pressure, which provides a controlled, uniform and deeper penetration of preservatives. Pressure treatment is primarily used on pine wood since it has a better ability to absorb the preservatives than spruce wood has. Moreover, preservatives are only absorbed by the sapwood and for better durability, the sapwood should be impregnated all the way into the heartwood. Impregnated sapwood of pine has significantly better resistance to fungal decay than heartwood of pine [3].

A classification for pressure treated wood in the Nordic countries has been established by the Nordic Wood Preservation Council, NTR based on the European standard SS-EN 335, for treated wood. In the European standard, different use-classes (UC) are formulated, depending on the expected environmental exposure of the wooden component with respect to moisture. There are five different use-classes; UC1 for indoor use and UC2 for sheltered elements. UC3 is for elements non-sheltered above ground and exposed to short-time moisture or frequent wetting. UC4 is for elements in contact with ground or freshwater exposed to permanent moisture and UC5 is for submerged elements in sea water [11, 12]. The Nordic NTR system is based on those use-classes which can be seen in Table 1. Treated wood labelled with NTR is quality controlled with regard to the quality of the final product, chemicals used, absorbed quantities, depth of penetration and associated environmental issues. The depth of penetration, chemicals used and the amount of preservatives in the material determine the grade of impregnated timber. The mechanical properties of treated wood are equivalent to untreated wood. [1, 5, 13].

According to NWPC Document No1:2017 stated by the Nordic Wood Preservative Council, materials treated with all kinds of chemicals should not be machined after treatment [14]. This is to prevent exposure of material with less preservative, which does not have the same protection against wood-destroying organisms as the treatment initially provided. If cutting, drilling or other minor machining cannot be avoided after delivery, machined surfaces must be treated with a suitable wood preservative. Timber that is machined after treatment, for example by planing or sawing, will lose its NTR classification.

12 Table 1: Classification of treated wood according to NTR based on the European standard for treated wood [1].

Classification Application Impregnation method

Pine wood in contact with Pressure impregnation. Full NTR-M seawater. penetration of sapwood. Pine wood in contact with ground or freshwater and constructions Pressure impregnation. Full NTR-A above ground that require extra penetration of sapwood. safety. Pressure impregnation. Full NTR-AB Pine wood above ground. penetration of sapwood. Pine wood above ground, finished Vacuum impregnation. A few mm NTR-B exterior joinery. penetration.

Wood preservation chemicals are divided into three main groups; oil-borne, water-borne and organic solvent-based preservatives. Nowadays, waterborne preservatives are the most commonly used, in the form of copper-based salt impregnation. Copper-based wood preservatives are used in class NTR-A and NTR-AB. They can also be used in NTR-B, but in this class, organic based impregnants are most commonly used. The most common oil-borne wood impregnant is creosote which is used in the class NTR-M [13, 15].

Impregnation and the use of impregnated wood is highly restricted in Sweden, since timber impregnated with arsenic, creosote, chromium and copper provides environmental and health hazards. The Swedish Chemical Agency (KEMI) sets the requirements and approves of different wood preservatives and the use of impregnated wood [16]. CCA preservatives (copper, chromium and arsenic) are nowadays forbidden to sell in the EU on account of the content of arsenic which is water soluble. Preservatives containing creosote are often used in moisture rich environment and marine environment because of their water repellant properties and toxicity to marine borers and fungi. Creosote is classified as carcinogen, i.e. having the potential to cause cancer, and are bio accumulative, which means that it can be stored in living tissue. Moreover, in Sweden creosote is highly restricted and only allowed for industrial use in railway timber or power line/telephone poles due to the health and environmental issues. Wood preservatives containing chromium are limited for use only in elements in contact with ground or water when the timber needs long-time protection.

According to regulations from The Swedish Transport Administration (Trafikverket) that sets the requirements for road and pedestrian bridges, chemical treatment of timber members is not allowed to contain chromium, arsenic or creosote [17]. The used chemicals for pressure impregnation in these applications are therefore mainly water-soluble copper-based salts. Salt-impregnated wood can be surface treated in the same way as untreated wood. As a result of environmental and health hazards, wood preservatives are likely to be even more restricted in the future and wood protection should then probably be favored over wood preservatives. Untreated wood can be durable in outdoor environment if designed appropriately with knowledge of climate conditions and material quality [7].

3.5 Glued laminated timber

Glued laminated timber, also referred to as glulam, is a refined timber product mainly intended for load bearing structural elements. The European Standard SS-EN 14080 sets the performance requirements of these products. Glulam is a structural element constructed of at least two lamellae that are glued together. The fiber direction of the lamellae should be tangential to the longitudinal direction of the product [18].

The manufacturing process of glulam is illustrated in Figure 6. Timber is sawn into lamellae and then dried in order to get a moisture content of 6-15%. They are then glued together. The moisture content is not allowed to exceed a difference of 5% between the neighboring lamella since this would cause a decrease in strength caused by possible crack initiations and torsion of the beam. Some amount of crack initiation will always be present in a timber material, but in general, they have no effect on the load bearing capacity of the structure [18].

After being dried, the lamellae are graded with respect to strength. This is done visually or by machine. According to the standard SS-EN 14080, the strength class of a single lamella is graded from T8-T26 where T8 is the lowest strength class [19]. The lamellae are thereafter finger jointed together to get longer pieces. The faces of the lamellae are then planed and coated with adhesive and pressed together parallel to each other. The lamellae should always be turned in the same direction with respect to the core. Moisture alterations may otherwise cause internal stresses of the laminate. The outer lamellae should, on the other hand, always

14 be turned with the core outwards. When the adhesive has set, the sides of the laminate are planed to get the desired dimensions and surface finish of the product [18].

Figure 6: The manufacturing process of glulam beams. Reference; Svenskt Trä, Design of Timber Structures - Volume 1 [32].

Glulam offers high strength with regard to their weight which enables it to be used over large spans. Concerning mechanical properties, glulam behaves in the same way as regular construction timber. As mentioned earlier, the material is orthotropic and the strength is reduced with increased moisture content. The material properties can still vary within the same component and between different components of the same material [18].

Laminated timber offers three main advantages. Firstly, the strength and Young’s modulus of the laminated product will usually be higher and more importantly, more uniform in quality compared to the original timber. For a regular timber element, strength is determined with respect to the weakest section of the material. The weakest section is due to defects in the timber, such as knots, splits, reaction wood or sloping grains which often result in increased stress when load is applied. In glulam, these are redistributed randomly throughout the laminate making it more uniform in quality, with less variability in strength than the original

15 pieces of timber. Secondly, the ability to use shorter lengths of timber, using the possibility to end-joint is appealing. In fact, glulam can theoretically be manufactured in an unlimited size, the limitation is rather the transportation of the finished products. Thirdly, the ability to create curved beams or complex shapes is also a benefit [3] [18].

The most common failure of a glulam beam subjected to bending is a tensile failure parallel to the fiber direction of the outer lamination. In this case, the failure point is often located in a knot or a finger joint. Splits and checks can also occur along the fibers when drying, which might reduce the strength [20].

Outer zone T22

Inner zone T15 B

Outer zone T22

Figure 7: Cross section view of a GL30c beam [1]

3.5.1 Timber structures: European standard SS-EN 14080

The standard SS-EN 14080:2013 provides the strength classes for glued laminated timber beams. CE classified glulam manufactured in Sweden, is dominating in strength classes GL30c, GL30h, GL28cs and GL28hs. The letters stand for c-combined glulam, h- homogenous glulam and s-split glulam beams. In homogenous glulam every single lamella is in the same strength class, and for combined glulam, the outer lamellae are in a higher strength class than the inner ones, see Figure 7. Beams are normally made from combined

16 glulam and pillars from homogenous glulam. The mechanical properties of the selected strength classes can be seen in the Table 2 [19, 21].

Table 2: The mechanical properties of glued laminated timber in strength classes GL28cs, GL28h, GL28hs, GL30c and GL30h [19].

Mechanical properties [MPa] GL28cs GL28h GL28hs GL30c GL30h

Bending strength parallel � 28,0 28,0 28,0 30,0 30,0 to fibers , Tensile strength, parallel � 19,5 22,4 22,4 19,5 24,0 to fibers ,, Tensile strength, � 0,5 0,5 0,5 0,5 0,5 perpendicular to fibers ,, Compression strength, � 24,0 28,0 28,0 24,5 30,0 parallel to fibers ,, Compression strength, � 2,5 2,5 2,5 2,5 2,5 perpendicular to fibers ,,

Shear strength �, 3,5 3,5 3,5 3,5 3,5

Rolling shear strength �, 1,2 1,2 1,2 1,2 1,2

Young’s modulus, parallel � 12 500 12 600 13 100 13 000 13 600 to fibers , Youngs’s modulus, characteristic, parallel to �, 10 400 10 500 10 500 10 800 11 300 fibers Young’s modulus, � 300 300 300 300 300 perpendicular to fibers ,

Shear-modulus � 650 650 650 650 650

3 Density [kg/m ] � 390 425 430 390 430

Density, characteristic � 430 460 480 430 480 [kg/m3]

The wood species mostly used for laminated products is spruce, but for structures that are going to be exposed to a moisture-rich environment, pressure impregnated pine can be used instead. The European standard SS-EN 14080 gives requirements for glued laminated products that are treated to withstand biological attack. For pressure impregnated glulam, the

17 lamellae are usually impregnated before planing and before being glued together. After the adhesive is set, the glulam is planed to get a homogenous surface, or it is left unplaned. An increased preservative effect can be obtained if surface treatment in form of penetrating oil is used. Another alternative is to impregnate the whole glulam element, but the possibility to do this is limited due to the size of the pressure vessel and the size of the glulam elements. It is important to note that glued laminated products cannot be classified according to the NTR grading system, only the single pressure impregnated lamellae can be classified. Pressure treated single lamellae glued together into a beam lose their classification because they are machined after treatment. For instance during planing, material with less preservative is exposed. Moreover, for impregnation of the whole glulam beam, the adhesive seam will limit the diffusion of preservative into the material [18, 22]. The adhesive seam will act as a barrier for the penetration of preservatives and a higher grade than NTR-B cannot be accomplished with this method. The requirements regarding the durability against biological attack according to SS-EN 14080 state that treatments that do not affect the strength, stiffness and density properties shall be used [19].

3.6 Durable design of timber structures

It is not unusual for timber to be used as construction material for smaller bridges. In Norway, timber bridges are common since use of creosote is permitted. Timber structures pressure treated with creosote are very durable and can serve a long time without much maintenance. In Sweden and the EU, creosote is not allowed to be used because of the health and environmental hazards [2]. However, timber bridges can be durable without the use of creosote. With a good and durable design that avoids high moisture content for long periods of time, in combination with a suitable preservative treatment, desired durability can be accomplished. There are similarities between the structure of a jetty and beam bridges built for pedestrian use today. In these bridges, the beams are often made of copper-based salt impregnated pine, built in an open design [23]. Because of this, glulam beams might be an alternative material for use in jetties.

18 3.6.1 Requirements and regulations

Requirements and design criteria in the EU are given by Eurocodes in order to specify how structural design should be conducted. For timber structures, this is given by Eurocode 5. National standards are also present in the form of adjustments of Eurocodes in a national perspective. In Sweden these are EKS 11 by Boverket regarding buildings and TSFS 2018:57 by Transportstyrelsen regarding roads and railways. Extensions of Eurocode and TSFS 2018:57 have also been used for bridges made by Trafikverket and are presented in TDOK 2016:0204. The most important parts related to moisture, preservative treatment and calculation of strength of timber structures are presented below. The following standards have been used:

SS-EN 1990 Eurocode – Basis of structural design

SS-EN1991-1-1 Eurocode 1: Action on structures

SS-EN 1995-1-1:2004 Eurocode 5: Design of timber structures

Part 1-1: General – Common rules and rules for buildings

SS-EN 1995-2:2004 Eurocode 5: Design of timber structures – Part 2: Bridges

SS-EN 1408:2013 Timber structures – Glued laminated timber and glued solid timber

SS-EN 335:2013 Durability of wood and wood-based products – Use classes: definitions, applications to solid wood and wood-based products

SS-EN 155228:2009 Structural timber – Structural timber preservative treated against biological attack.

TSFS 2018:57 The Swedish Transport Agency's regulations and general advice on the application of Eurocodes. “Transportstyrelsens föreskrifter och allmänna råd om tillämpning av Eurokoder”

TDOK 2016:0204 Swedish Transport Administration – Requirements for bridge construction. “Trafikverket -Krav brobyggande”

EKS 11 National Board of Housing, Building and Planning – Design Rules. “Boverkets konstruktionsregler”

19 3.6.2 Moisture

In timber structures, the moisture content has a significant role in the properties of glulam. It does not only act as a risk factor concerning fungal decay, but also influences both strength and stiffness. Therefore, when designing timber structures, this must be taken into consideration. In an outdoor climate in Sweden, the moisture content is normally between 14% and 20%. Timber used outdoors and in marine environment above the water level will serve in a moisture rich environment. Requirements and regulations of the design of timber structures are defined in Eurocode 5, SS-EN 1995-1-1. It states that structures should be assigned to one of the service classes 1, 2 or 3 [24]. In the case of beams used outdoors unprotected against precipitation or in contact with the ground, service class 3 is to be assigned. For timber used in service class 3, the average moisture content in most softwood will exceed 20% [18]. Considering these regulations, timber used in a marine environment above the water line should then serve in service class 3 and will periodically have a moisture content above the fiber saturation point [9].

Timber structures are capable of a long service life if designed in a suitable way. Essentially, timber will not rot if the moisture content is below the fiber saturation point. Timber used outdoors and in marine environment above the water level will periodically have a moisture content above the fiber saturation point. A high moisture content may also occur locally in the timber at member junctions, where moisture and dirt easily can get trapped and lead to premature fungal decay. To minimize the risk of a high moisture content and biological attack, good detailing such as drainage and air circulation at such points can help. To protect the structure, some basic principles should be followed to improve the durability [9]:

• Provide effective drainage from timber and ensure the surfaces are well ventilated: Moisture exposed timber members need the opportunity to dry in order to prevent a high moisture content for a long period of time.

• Protect the top of the horizontal members: Horizontal faces of timber are at risk for standing water. Consequently, this can lead to fungal or insect attack if the moisture content exceeds the fiber saturation point for long periods of time. These areas can be protected by, for example, designing a fall angle on the horizontal surfaces that will minimize the volume of accumulated water. Rounded corners can also be used, as they make water drain off the surfaces better,

20 since they help maintain surface tension and pull the water off the horizontal face. Most importantly, the horizontal members should have the opportunity to dry after exposure to moisture.

• Protect exposed end grain and avoid capillary paths: Water can easily be absorbed by capillary action and be transported further into the timber, resulting in an increased moisture content. Capping of the end grain will give a protection against moisture exposure and thus reduce the risk of fungal decay.

• Avoid direct contact with other absorbent materials.

• Avoid water traps.

In the matter of bridges, Trafikverket sets the requirements for road and pedestrian bridges, which are formulated in “TDOK 2016:0204”. It states that a structural element of a bridge should be protected against weather exposure to the extent that the moisture content in the timber is controlled and maintained at a level of which rot cannot occur. Timber in contact with moisture should therefore have the opportunity to dry. The construction should also be designed in a way that prevents accumulation of water and dirt. For bridges, structural elements should be situated at least 800 mm over the ground or at least 500 mm over the average water level [17].

3.6.3 Marine Environment

Timber structures in marine environment need to be designed for variable surrounding conditions, ranging from precipitation and spray from the sea, to cyclic wetting and drying, to moisture saturation. When designing timber structures, the sea level plays a significant role and needs to be taken into consideration. The sea level varies and is dependent on the tidal cycle, wind and waves. The structure should be designed so it does not come in direct contact with the sea, since marine boring organisms attack in the water line and can cause severe damage. Wetting from the sea in form of spray and splashing does actually have some benefits, since the salt tends to prevent the wood decaying fungi to grow. A high salt decomposition will inhibit the growth of fungi and act as a wood preservative [9, 10]. So, for timber located in a marine environment above the water line, precautions with respect to the salt content is not needed. The highest concern in this area is rather that the timber will be highly exposed to wetting. As a result of this, high moisture content will periodically be

21 present in the timber. Also of importance, regarding the steel components that are used in timber construction, such as fixings and fittings, saltwater will cause corrosion. It is therefore advisable to use stainless or galvanized steel.

3.6.4 Preservative treatment

Chemical pressure treatment should not be a substitute for a good design and structural wood protection. Nevertheless, pressure impregnation will give an increased lifetime and be an effective form of wood preservation. The structural elements that are considered in this thesis will be subjected to a harsh and moisture rich environment with cyclic wetting from precipitation and spraying from the sea. To obtain resistance to biological organisms, SS-EN 1995-1-1 states that timber shall either have adequate natural durability or be given a suitable preservative treatment [25]. Accurate preservative treatment is depending on the use-class that the timber structure is subjected to. According to the formulation of use-classes in chapter 3.4, the timber element this thesis aims to consider goes under UC3. The timber component is not covered and not in contact with the ground. It is either continually exposed to the weather or is protected from the weather but subjected to frequent wetting [9]. Moreover, Trafikverket (TDOK 2016:0204) states that for bridges located in a marine or a road traffic environment, salt and moisture will be present in the wooden structure. Therefore, UC4 should be attributed to preserve the structure from fungal decay and wood destroying insects according to SS-EN 335-2 and SS-EN 351-1 [17].

Preservative treatment is not allowed to contain creosote, chromium or arsenic [17]. The preservative treatment used is therefore a water-soluble copper-based salt impregnation where additional agents such as boron can be present [2]. Also, additional preservatives should be applied if machining has been done after pressure treatment. For instance, penetrating oil can be used to increase the preservative effect on the wooden surface [18].

22 3.7 Service life

Service life of a timber design is difficult to predict due to the wide variety of biological processes that are involved in the deterioration process. Currently, there is no quantitative method to estimate the deterioration and service life of timber members. Assessment of material performance and prediction of expected service life are well established for other construction materials, for example concrete. Service life models for concrete take into account carbonation, corrosion and other deteriorating mechanisms. For timber, neither the standard for the design of timber structures, Eurocode 5 SS-EN 1995-1-1, nor the specific standard for timber bridges SS-EN 1995-2 currently has a quantitative method to estimate the deteriorating process of timber members [24, 26]. Nevertheless, there are some parameters such as design and material properties that will increase the risk of high moisture content for long periods of time. This could possibly lead to premature fungal decay.

There is a lot of ongoing research in this field in order to develop a quantitative method to estimate the deterioration process of timber. In a project performed by RISE on the subject “Durable Timber Bridges”, a service life model has been established to serve as a guideline to evaluate the expected service life of timber members in bridges [2]. The service life of a timber structure, with respect to fungal decay used in use class 3, is dependent on a range of variables such as: geographical location, local climate conditions, sheltering from rain, design, distance from ground, material used and severity class. By having the knowledge of these influencing parameters, an expected service life could be determined. The results of service life calculations are meant for construction design and risk assessment of future wooden structures.

This method was based on a reference element. A horizontally exposed plane board of untreated spruce, without any moisture traps exposed to outdoor conditions in terms of rain, moisture and temperature. According to Pousette et al [2], the expected service life estimated in years can be calculated with eq. 1. The influencing of material resistance is expressed in the factor �, the characteristic annual exposure to rain and moisture is expressed in the factor

� and the severity factor �. The expected service life can then be determined for an optional timber part by using corrected factors with respect to the reference element for the influencing variables.

23 �� = [��] (1)

� - Material resistance

� - Characteristic annual exposure

� – Severity factor

3.7.1 Required service life

The required service life of a structural design is suggested in the Swedish standard SS-EN 1990 for different areas of usage and can be seen in the Table 3 [27]. Moreover, according to TDOK 2016:0204, a wooden bridge is to be designed for a service life of 40 or 80 years [17].

Table 3: Indicative design service life according to SS-EN 1990 [27]. Design service Indicative service life Example life category [years] 1 10 Temporary structures

2 10 - 25 Replaceable structural parts

3 15 - 30 Agricultural and similar structures Building structures and other common 4 50 structures Monumental building structures, bridges and 5 100 other civil engineering structures

3.7.2 Severity class

A severity factor � is introduced (see Table 4) to ensure a reliable design that meets the requirements for the expected service life. The severity factor is dependent on the consequence of damage related to decay. For load bearing structures where there is risk of human injury, the highest severity class should be considered. For elements that are easy to replace, like for example cladding and decking, a low to medium severity class can be considered, depending on the possibility of replacement [2].

24 Table 4: Definitions of severity classes for durability [2].

Severity class Example �� Where it is accepted and easy to replace a limited number of Low components if decay should be initiated within expected 0,6 service life When the expected economical and practical consequences are Medium 0,8 significant High Where there is a risk for human injuries or loss of lives. 1,0

3.7.3 Exposure conditions

Timber structure used outdoors are exposed to wetting. As long as free water does not occur in the timber member, decay will not occur. A structure can be protected from precipitation by sheltering design, but risk of leakage should also be considered. Free water can be a result of rain, splashing, spraying and run-off water. Depending on the geographic climate, location, sheltering and design, the annual exposure dose of free water caused by precipitation can be determined in eq. 2 [2].

� = � � � � � � (2)

� – annual reference exposure dose depending on geographic location

� – factor describing the effect of local climate conditions

� – factor describing the effect of sheltering

� – factor describing the effect of distance from ground

� – factor describing the effect of detail design

� = 1,4 (calibration factor)

�: The annual reference exposure dose describes how the climate in a specific geographic location affects timber exposed to precipitation, temperature and moisture. The moisture content in wood has been calculated using climate data. The annual reference exposure dose has been determined in forms of geographic zones and is illustrated in Figure 8 [2]. The value of � corresponding to the color in Figure 8 is defined in Table 5.

25 Table 5: Specifies the annual exposure dose � for different zones. The different zones are defined in Figure 8 [2].

Annual exposure dose DE0 (days) Zone Color code Mean Range a 66 63-29 b 60 57-63 c 55 52-57 d 49 46-52 e 43 40-46 f 37 34-40 g 32 29-34 h 26 23-29 i 20 17-23 k 15 12-17 m 9 6-12

26 26

h g

f d a c e b m

Figure 8: Zones for Europe for estimation of annual exposure dose [2]

Figure 2.5. Zones for Europe for estimation of annual exposure dose �: The local climate conditions are considering the vertical surfaces and the risk of driving rain. Free driving rain is present when rain and hard wind occur at the same time, making the rain move vertically. This is mainly a concern for the part of the timber facing the wind direction since they experience the most severe exposure. Protection from free driving rain from surrounding buildings, vegetation etc. should also be taken into consideration. Timber parts

exposed to free driving rain without shelter should be considered to be severely exposed with

�=1. A reduction of the factor can be done if surrounding protection is present or if the frequency of free driving rain is low, this is defined in Table 6. The frequency of free driving rain is mapped in Figure 9, where free driving rain should be considered in zones with an index > 1,6. It should be noted that horizontal surfaces without protection from rain should always be considered to be under severe exposure [2].

Table 6: The effect of driving rain and on vertical wood surfaces. Degree of Example � exposure �� Light Driving rain is not expected and protection is present. 0,8 Driving rain is expected and protection is present. Medium or 0,9 Diving rain is not expected and protection is not present. Severe Driving rain is expected and protection is not present. 1,0

28 29

Figure 9: The intensity of free driving rain in Europe [2]

Figure 2.7. Map indicating intensity of free driving rain over Europe in the form of an index. For zones with�: index higher than 1,6 driving rain can be regarded as frequent, while in zones with index less thanDescribes 1,6 effect the of effect driving of rainsheltering. can be Thisneglect factored in is Table dependent 2.4. on the width of the overhang (e) and the distance from the shelter (d) to the part or detail that is considered, see Figure 10. It is

assumed that the shelter e.g. the deck is watertight so that no water can pass through the deck.

29 The ratio between e and d determines the sheltering effect factor by eq. 3 or 4. For a freely exposed element kE2=1.

� = 1 − 0,2 if 0 < < 1 (3) � = 0,8 if > 1 (4)

Figure 10: Definitions of overhang e, distance d and distance from ground a.

�: Describes the effect of distance from ground [2]. Timber parts that are closer than 400 mm from the ground will experience splashing rain from the ground which will increase the moisture content in the wood. This factor assumes that the timber part is not in direct contact or less than 100 mm from the ground, since such designs are not suitable due to expected premature fungal decay. A question that might be asked is, what is the definition of ground? Is it the actual soil or, for example, the concrete that supports the timber part? An arbitrary answer is if the splashing from rain on the concrete causes an increased exposure to moisture, the distance between the concrete to the timber should be considered instead. � is calculated by eq. 5 or 6.

� = if 100 �� < � ≤ 400 �� (5)

� = 1 if � > 400 �� (6)

�: Describes the effect of detail design and is summarized in Table 7 below. These results are based on field test that have been carried out by Pousette et al [2] in the project “Durable Timber Bridges”. In Table 7, different common detail designs are presented and listed in six different severity classes, ranging from excellent design to poor design with respect to moisture exposure. For details that are not presented in Table 7, an arbitrary value should be chosen, based on the degree of water exposure and the possibility to dry to avoid water getting trapped in the structure. Trapped water will locally increase the moisture content in the timber part and consequently increase the risk of fungal decay.

31 32

Table 7: Values of � depending on detail design with respect to exposure to moisture [2]. Table 2.5. Rating of details with respect to exposure.

Class Description Example kE4

Design characterized by excellent Excellent ventilation (air gap > 10 mm) and no 0,8 standing water. For example: a vertical surface without connecting members or with sufficient gap between members1

Design characterized by excellent Good ventilation but standing water after 1,0 rain events. For example: horizontal surface without connecting member.

Design characterized by poor Medium ventilation but limited exposure to 1,25 water. For example, vertical contact areas without sufficient air gap.

Design characterized by poor ventilation and high exposure to water Fair or end-grain with good ventilation and 1,5 limited exposure to water.1 For example: horizontal contact areas and end-grain with sufficient air gap.

Design characterized by exposed end- Poor grain with no ventilation and very high 2 exposure to water. For example: end- grain contact area without air gap.

1) It is assumed that the gap is kept completely free from dirt and vegetation

For details different from the examples shown, the user must assess the degree of moisture �:exposure and relate to one of the five classes listed in Table 2.5. The main criteria should be the degree of rain exposure and the possibility of fast drying to avoid moisture traps. In case Theof calibrationuncertainty factora more � severe= 1, 4class has shouldbeen verified be chosen by. Pousette et al [2] based on how well the expected service life corresponds to studied cases from real bridges where the performance In evaluating details, the risk of soil and dirt being trapped in critical spots should be relatedconsidered. to decay Another is known. risk couldThe c alibrbe thatation vegetation factor � w illwas lead set to to increased a value w riskhere of the moisture result beingof the expectedtrapped. service life gave an adequate safety margin compared to the observed performance of Annexthe selected A shows cases. a few A examples high safety of how margin the grading was required can be performed. since the method is intended for timber bridges and the consequence of failure of a load bearing element would be devastating. Note again that timber which is sheltered from rain, for example by protective cladding or sheltering from elements above, is not dealt with here. For this case see Section 2.6.

32 3.7.4 Material resistance �

Another important and influencing factor is the material resistance to fungal decay. This is depending on the materials' wetting abilities and their natural resistance to fungal decay. These properties depend on the wood species used, and the use of any potential wood preservative. Values of the most commonly used materials for these applications are presented in Table 8 below [2].

Table 8: The material resistance dose � in number of days are presented for selected and commonly used materials in bridge construction.

Wood Species �� (days)

Norway spruce 325

Scots pine sapwood 300

Scots pine heartwood 850

Preservative-treated wood NTR-AB 1700

Preservative-treated wood NTR- A 2600

By determining the influencing factors, the expected service life can be determined by eq. 1. The expected service life is then compared to the required service life to see if it meets the requirements. If not, modifications of the design or material used will be needed to increase the lifetime of the timber component.

3.8 Case study

This thesis aims to evaluate the possibilities of using glued laminated timber as a load bearing structural element for jetties and pedestrian bridges in a marine environment. As mentioned in the introduction, steel beams are most commonly used for jetties and pedestrian bridges, but for this purpose, glulam beams can be a valid alternative. A structure made entirely of wood would reduce the amount of material used for cladding, since there are no steel beams to hide. A reduction of material would benefit the environment and most likely also decrease the cost. In this case study, one specific case has been adapted to evaluate the possibilities to exchange the steel beams for glulam beams. The specific case is presented in Figure 11 and in the introduction in Figure 1-3. It shows a pedestrian jetty, designed by Ramboll Sweden AB,

33 located in Lysekil on the Swedish west coast. It is located close to the sea in a moisture rich environment. The current structure consists of three steel beams made of HEB 300 supporting secondary timber beams and a wooden deck. The steel beams that can be seen in Figure 11 span a distance of 8.5m and the width of the deck is 2.5m. The structure is located 1.25m over the mean sea level. The design of the structure can be seen in Figure 12 and 13. The glulam structure will consist of two beams instead of three to avoid an overdetermined problem.

Figure 11: Pedestrian bridge designed by Ramboll Sweden AB and also the structure which the case ANVISNINGAR FÖR KRAV PÅ MATERIAL, UTFÖRANDE OCH study is based on. KONTROLL, SE TEKNISK BESKRIVNING. KOORDINATSYSTEM: SWEREF 99 12 00 HÖJDSYSTEM: RH 00

HÄNV ISNINGAR TILLVERKNINGSRITNINGAR FÖR STÅLBALKAR SE RITN. K- 24- 6- 121 OCH K- 24- 6- 122

P.A D E F K- 20- 2- 123 K- 20- 2- 123 K- 20- 2- 123 EXTRA REGEL 8500 8450 300 VID RÄCKESSTOLPE HÖJD ANPASSAS +1.55 GL A CI S SÅ GA S L OKA L T TILL BEF. MARK OM STÅLBALKAR INTE KAN PLACERAS ENL. ANVISNING. HHW +1.21 ca. +1.21

UPE160 +0.96 1:50 L120x80x10 +0.79 MHW + 0 . 6 9 HEB300 1:50 UPE160 EXTRA REGEL +0.62 VID RÄCKESSTOLPE HEB300

HEB220 +0.32 SVETSAS TILL PÅLES TRYCKPLÅT ENL. BEF. GLACIS BEF. MASSOR URSCHAKTAS DETALJ 2- K- 20- 6- 122 FÖR GJUTNING AV BETONGBALK. MW - 0 . 2 9 D 0 0

K- 20- 2- 123 1 1 / / 0 0 7 2 2 2 E E

L BEFINTLIG FYLLNING L Å Å P P S S

ML W - 0 . 9 7 R R Ö Ö R R L L Å Å T T S S

LLW - 1.43

UNGEFÄRLIG BOTTENNIVÅ

SKYDDSRÖR AV PLAST ANTAGEN BERGNIVÅ UTANPÅ PÅLAR, I GJUTES. BEF. KALLMUR AV GRANITBLOCK

E F SEKTIONFigure C 12: Design of selected part of pedestrianK- 20- 2- 123 jetty on which the case study is based.K- 20- 2- 123 1 : 20

a BET ÄNDRINGEN AVSER DATUM SIGN

e d RELATIONSHANDLING

l HAVSBADSPARKEN l e 34

d o LYSEKILS KOMMUN

2 Ramböl l Sv er i ge AB

0 Vädur sgat an 6

1 Box 5343

6 402 27 Göt eborg

2 Tf n 010 - 615 60 00

\ a www.r ambol l .se

\ UPPDRAG.NR RITAD/KONSTR. AV HANDLÄGGARE

G 1320024047 D. SAXBERG J. SANDBERG

\ : DATUM ANSVARIG O 2017- 06- 30 MI CHA EL SÄ F

0 ETAPP 1 - NYA BRYGGOR

5 SEKTIONER - PROMENADBRYGGA

7 SKALA 1: 20

2 SAMMANSATT REDOVISNING

6 SKALA NUMMER BET

0 00,1 0,5 1, 0 1, 5 2,0

7 A1 1: 20

0 MET ER K-20-2-122

2 A3 1: 4 0 ANVISNINGAR FÖR KRAV PÅ MATERIAL, UTFÖRANDE OCH KONTROLL, SE TEKNISK BESKRIVNING.

KOORDINATSYSTEM: SWEREF 99 12 00 HÖJDSYSTEM: RH 00

HÄNV ISNINGAR TILLVERKNINGSRITNINGAR FÖR STÅLBALKAR SE RITN. K- 24- 6- 121 OCH K- 24- 6- 122

UPE160 +0.96 1:50 L120x80x10 +0.79 MHW + 0 . 6 9 HEB300 1:50 UPE160 EXTRA REGEL +0.62 VID RÄCKESSTOLPE HEB300

HEB220 +0.32 SVETSAS TILL PÅLES TRYCKPLÅT ENL. BEF. GLACIS BEF. MASSOR URSCHAKTAS DETALJ 2- K- 20- 6- 122 FÖR GJUTNING AV BETONGBALK. MW - 0 . 2 9 D 0 0

K- 20- 2- 123 1 1 / / 0 0 7 2 2 2 E E

L BEFINTLIG FYLLNING L Å Å P P S S

ML W - 0 . 9 7 R R Ö Ö R R L L Å Å T T S S

LLW - 1.43

UNGEFÄRLIG BOTTENNIVÅ

SKYDDSRÖR AV PLAST ANTAGEN BERGNIVÅ UTANPÅ PÅLAR, I GJUTES. BEF. KALLMUR AV GRANITBLOCK Figure 13: Close up of the design illustrated in Figure 12. E F SEKTION C K- 20- 2- 123 K- 20- 2- 123 1 : 20

n e 3.8.1 Preservative treatment

a BET ÄNDRINGEN AVSER DATUM SIGN

e d RELATIONSHANDLING

M The structural element that is considered in this thesis will be subjected to a harsh and

l HAVSBADSPARKEN

d o LYSEKILS KOMMUN

K moisture rich environment. The glulam beams designed to withstand the prescribed load will

4 serve in UC3. It is not covered and not in contact with the ground but will be subjected to

2 Ramböl l Sv er i ge AB

0 Vädur sgat an 6

1 Box 5343

6 402 27 Göt eborg

0 frequent wetting [9]. This would then correspond to a pressure impregnation in class NTR-

2 Tf n 010 - 615 60 00

\ a www.r ambol l .se

\ UPPDRAG.NR RITAD/KONSTR. AV HANDLÄGGARE

G 1320024047 D. SAXBERG J. SANDBERG

\ : AB, see Table 1. According to Trafikverket (TDOK 2016:0204), bridges in a road traffic or DATUM ANSVARIG O 2017- 06- 30 MI CHA EL SÄ F

0 ETAPP 1 - NYA BRYGGOR

5 SEKTIONER - PROMENADBRYGGA

: marine environment should be assigned to UC4 [17]. UC4 is for elements in contact with

7 SKALA 1: 20

2 SAMMANSATT REDOVISNING

6 SKALA NUMMER BET

0 00,1 0,5 1, 0 1, 5 2,0

7 A1 1: 20

0 ground or freshwater exposed to permanent moisture which will correspond to a pressure MET ER K-20-2-122

2 A3 1: 4 0 impregnation in class NTR-A. However, in this specific case (Figure 11) the application of UC3 is accurate since the case is not defined as a bridge.

The glulam beams will be made of pine wood since it easily absorbs the preservatives into the sapwood. The preservative treatment is not allowed to contain creosote, chromium or arsenic. The used preservative treatment is therefore a water-soluble copper-based salt impregnation. The copper-salt impregnation will not protect the glulam beam from splitting and checking. This needs to be taken into consideration and suitable design and surface treatment should be applied. Also, additional preservatives should be applied if machining has been done after pressure treatment, penetrating oil could, for instance, be used.

35 3.8.2 Calculations of strength and deflection

The calculations of the glulam beam will be done in ultimate limit state ULS and serviceability limit state SLS. This will be done with regard to bending strength, shear strength and the deflection of the beam. The calculations are done by the partial factor method described in SS-EN 1990-1-1 [27] and more specifically for timber in SS-EN 1995-1-1 [24]. The structure will be subjected to permanent loads in form of the self-weight of the structure and a variable load that is not always present. The current structure is designed for variable loads categorized in the class C5 from to SS-EN 1991-1-1, chpt. 6.3.1.2 [25]. This class is applicable for places where big crowds can occur at the same time. The load case of the structure is:

• Variable loads: 5 kN/m2 • Permanent loads in form of weight

Definition of load parameters The load case and corresponding load factors were collected from the calculations of current steel beams made by Ramboll AB. The same load factors are used for the timber structure. The severity factor for the load bearing element is class 3, which is the highest.

In ULS, the structure is designed to withstand the worst-case scenario of loads occurring at the same time. Calculations performed in SLS do not assume that the maximum of all the loads occur at the same time. The load combination factors are therefore introduced to get a plausible combined value for different load cases. The load combination factors are specified for different load categories [28].

� = 1.0 Partial factor regarding severity class 3

�, = 1.5 Load factor, variable load in ULS

�, = 1.35 Load factor, permanent load in ULS � = 0.89 Reduction factor for permanent load at unfavorable load.

� = 0.7 Load combination factors in SLS (category C)

� = 0.6 Load combination factors in SLS (category C)

36 Definition of material parameters for timber Timber is a biological and natural material. In comparison to steel, it has considerable variability regarding its properties. Some of the properties that are specific for timber products, and influence its qualities, include type of load, duration of load, partial factors for material properties and wood moisture content which depends on service class.

The moisture content in wood has a significant role, since it influences both strength and stiffness. To take this into consideration when designing, one of the service classes 1, 2 and 3 is assigned. The structure will in this case be categorized in service class 3.

Timber also shows a significant reduction of strength over time. To consider the reduction of strength, different load duration-classes are defined, regarding how long the load will be present. The load-duration ranges from permanent load via short-term load to instantaneous load [24]. In this specific case, the structure will be subjected to permanent loads in form of self-weight and variable loads classified as short-term loads. Short term load is defined as being present less than a week.

Since the load-duration and moisture content both reduce the strength of the material, the load-duration and the service class are combined in a factor kmod which is a reduction factor of the characteristic strength of timber [29]. In this case, � = 0.7.

Moisture also influences the deformation of timber. Higher moisture content will lead to more deformation in form of creep. This is expressed in factor kdef. In this case � = 2.0 since the timber element is subjected to service class 3. Regarding shear strength, a reduction factor

� = 0.65 for glulam is used in service class 3. This factor considers the appearance of splits and cracks in the timber element caused by moisture-related stresses that reduce the width, b, of the glulam element [29].

To take into consideration both the uncertainties of the strength model used in designing and the dimensional variations of the material, a material factor γM is introduced [29]. By dividing the characteristic strength with this factor, the design strength of the material can be determined. This can be seen in eq 11.

37 � = 1.25 Partial factor for the material property, glulam

� = 2.0 Factor regarding service class 3

� = 0.7 Factor regarding short-term load and service class 3

�, = 28.0 �� Characteristic bending strength from Table 2

�, = 3.5 �� Characteristic shear strength from Table 2

� = 0.65 Reduction factor for service class 3, regarding shear

� = 1.0 Promotion factor regarding the volume effect. Depends on the height, h

3.8.3 Calculation of glulam beam in ULS

The calculations will be based on a simplified model of the case presented in Figure 11. Only one beam will be considered and the deck and studs are assumed to be equally distributed over the top surface. Torsion of the beam will therefore not be taken into consideration.

Qdim

Figure 14: Simplified model of the load case on which the calculations are based.

In ULS, the beams are designed to withstand stresses caused by bending and shear. The model in Figure 14 is an elementary case. The maximum bending moment for this case is defined in eq. 7. The maximum shear stress for a rectangular cross section is defined in eq. 9, where Wy is the section modulus and V is the shear force.

� = (7)

� = (8)

� = (9)

38 According to the partial factor method described in SS-EN 1990-1-1 chpt. 6.4.3, the design load in this case should be load combination b [27]. The variable load will be much larger than the permanent load, and therefore load combination b is addressed. The design load combination is used in ULS and is defined in eq.10.

� = � � �, � + � �, � (10)

The design value of bending strength is determined by eq.11.

, �, = � (11)

The design value of the shear stress is defined in eq.12.

� = �,� (12)

3.8.4 Calculations of the glulam beam in SLS

The calculation in SLS is done regarding the deflection of the beam. Calculations in SLS are important to maintain visual appearance and functional demands within the limitations and to prevent damage, brittle fracture and limit the effect of creep. The maximum deflection of the beam of the elementary case, Figure 14, is defined in eq.13.

� (0.5�) = (13)

When determining the deformation of a structure, relevant load combinations need to be defined. These are defined as the characteristic combination, frequent combination, and quasi- permanent combination. Deformation in SLS for timber element should be calculated for the characteristic and the quasi-permanent combination, according to SS-EN 1995-1-1 [24]. The instantaneous deformation, � should be calculated with the characteristic combination of actions using mean values of the appropriate moduli of elasticity. The final deformation over time influenced by creep can be obtained by reducing the stiffness of the material when calculating. This can be seen in eq.14. The final deformation, � should be calculated for

39 the quasi-permanent combination of actions. With only one variable load present, the equations for instant deflection and final deflection can be defined as eq. 15-18, where G is permanent loads and Q is variable loads.

�, = (14)

� = �, + �, (15)

� = �, + �, (16)

�, = �,(1 + �) (17)

�, = �,(1 + ��) (18)

The design value of deflection is not the same for instant deflection and final deflection. The final deflection is allowed to be larger. According to Transportstyrelsen TSFS 2018:57 [30], the maximum allowed instant deflection of loads on pedestrian bridges can be seen in eq.19. According to SS-EN 1995-1-1 chpt. 7.2 [24], the maximum allowed deflection over time, affected by creep can be seen in eq.20.

� = (19) , � = (20) ,

The possibility of replacing the current steel beam with glulam beams will be evaluated. An analysis of the market for pressure impregnated glulam will be done to see what dimensions are available, what preservative classification is possible, and which producers there are in Sweden. Calculations of strength of suitable glulam beams in this specific case will be done to determine suitable dimensions of the beam. An estimation of the expected service life will also be done by the method presented in chapter 3.7.

40 4 Results

The results will be presented below. Firstly, findings from the literature study will be summarized. An analysis of the existing market for pressure impregnated glulam in Sweden will then follow. Calculations in ULS and SLS regarding the case from the case study will be presented thereafter and finally, evaluation of the expected service life of the glulam beams from the case study will be performed.

4.1 Literature study

• The marine environment, above the water line, is moisture rich with precipitation and frequent wetting from the sea. Service class 3 is assigned. The average moisture content will periodically exceed 20%. • A high moisture content reduces the strength and stiffness of the material. • With a high moisture content above the fiber saturation point, fungal decay can occur. • The salt content of the sea has no negative effect regarding fungal decay. Rather, salt acts as wood preservative. • Timber placed under sea level will be attacked by shipworms. Shipworms can cause severe damage in a short period of time. Therefore, the timber element needs to be placed above the water line with a minimum distance of 500mm to the mean water level. Tidal cycles also need to be taken into consideration. • Geographic location, local weather and environment affect the susceptibility to fungal decay. • The structural elements in the current environment are not in contact with the ground but subjected to frequent wetting, and thus UC3 will be assigned. • UC3 corresponds to a pressure impregnation of class NTR-AB. • The chemical treatment of glulam beams is not allowed to contain chromium, arsenic or creosote. The preservative treatment used is a copper-based salt impregnation together with suitable surface treatment, for example penetrating oil. • Structural wood protection should be used together with preservative treatment. Good detailing can reduce the moisture content in the wood and prevent the occurrence of fungal decay. This can be done by minimizing the risk of water getting

41 trapped, protecting the end grain and ensuring moisture exposed timber gets the opportunity to dry. • Glulam beams cannot be classified in the NTR-system. This is due to two reasons. Firstly, the adhesive seam limits the diffusion of preservatives into the material. Secondly, planing of the beam will expose surfaces with less preservatives than impregnation initially provided.

4.2 On the market

Currently, there are three certified producers of glulam in Sweden; - Martinson Group AB - Moelven Töreboda AB - Setra Trävaror AB

Listed below in Table 9-11 are pressure impregnated glulam products available on the market in Sweden. The quality, dimensions, impregnation class and type of impregnation available from Swedish producers are included in the list. It should be mentioned that glulam beams cannot be classified in the NTR system. Nevertheless, to determine the service life of the beam, an impregnation class needs to be assigned. Based on a dialogue with the producers, a corresponding impregnation class has been assumed.

Martinson Group AB Table 9: Available pressure impregnated glulam beams from Martinson Group AB. Corresponding Dimensions (mm) Quality Type of impregnation impregnation class of beam*

90 x 90 GL28h Whole beam NTR-B

115 x 115 GL28h Whole beam NTR-B

140 x (33 x n**) GL28h Lamella (NTR-A) NTR-AB

215 x (33 x n**) GL28h Lamella (NTR-A) NTR-AB

* The corresponding impregnation class is an assumption based on a dialogue with the producers. **n is the number of lamellae multiplied with the height of one lamella.

42 Pressure impregnated glulam beams are available in the strength class GL28h. The smaller beams are impregnated after being glued together. The impregnation performed will correspond to impregnation class NTR-B since the adhesive seam will prevent the preservatives to fully impregnate the sapwood. Martinson Group AB also carry larger beams where the lamellae are pressure impregnated before being glued together. These single lamellae are impregnated in class NTR-A. The lamellas are then glued together and planed, which results in loss of classification. The planed beam will therefore have a corresponding pressure impregnation of NTR-AB.

There is a limited number of dimensions of pressure impregnated beams carried by Martinson Group AB. They are produced in the width of 140 mm or 215 mm, but the height of the beam can vary depending on demand. The possible height of the beam is however depending on the height of a single lamella which is 33 mm.

Moelven Töreboda AB Table 10: Available pressure impregnated glulam beams from Moelven Töreboda AB. Corresponding Dimensions (mm) Quality Type of impregnation impregnation class of beam*

90 x 200 GL30c Lamella (NTR-AB) -

90 x 300 GL30c Lamella (NTR-AB) -

Any dimensions GL30c Lamella (NTR-AB) - can be ordered** *The corresponding impregnation class is an assumption based on a dialogue with the producers. ** Any dimensions of pressure impregnated glulam beams can be ordered, selected from normal dimensions of untreated glulam beams. However, the width has to have a minimum of b=90mm.

Pressure impregnated glulam beams from Moelven Töreboda AB can be ordered in any dimension from the ordinary non-impregnated glulam dimensions. The lamellae are impregnated in impregnation class NTR-AB before being glued together. After gluing, the beams are planed and lose their impregnation class. A corresponding impregnation class cannot be assumed in this case.

43 Setra Trävaror AB Table 11: Available pressure impregnated glulam beams from Setra Trävaror AB. Corresponding Dimensions (mm) Quality Type of impregnation impregnation class of beam*

90 x 200 GL30c Whole beam NTR-B

90 x 300 GL30c Whole beam NTR-B

*The corresponding impregnation class is an assumption based on a dialogue with the producers.

Pressure impregnated glulam beams from Setra Trävaror AB are available in two different dimensions as seen in Table 11. The whole glulam beam is pressure impregnated. The adhesive seam will then prevent the preservative to fully impregnate the wood. Thus, the corresponding impregnation class will be NTR-B.

4.3 Case study

The possibility of replacing the current steel beam with glulam beams will here be evaluated regarding bending strength, shear strength and the deflection of the glulam beam. Based on the analysis of the market of glulam beams, the dimensions of a glulam beam from Martinson Group AB has been chosen. The strength class of the beam is GL28h and the dimensions are 215x594 mm. The results of the calculations of strength and deflection are presented below. For complete calculation see Appendix A. Material parameters, load factors and equations used in the calculation of strength and deflection of the glulam beam can be seen in chapter 3.8.

Dimensions and data GL28h Strength class � = 8.5 � Length of beam � = 0.215 � Width of beam ℎ = 0.594 � Height of beam

� = 1.25 � Width of the deck spanning over one beam

44 Load The structure will be subjected to both variable loads and permanent loads (in the form of self-weight of the structure). The variable loads are categorized in the class C5. The permanent load is the sum of the weight of the deck, studs and the weight of the glulam beam itself.

Permanent load:

�, = �, + �, + �, = 0.87��/� (21)

Variable, distributed load: � = 5.0 ��/�

� = � � = 6.25 ��/� (22)

4.3.1 Calculation in ULS

The design load is determined by eq.10, where the permanent loads are determined in eq. 21 and the variable load from eq. 22. This gives the value;

� = 10.43 ��/� (23)

The maximum bending moment was calculated by eq. 7 and determined to be;

� = 94.2 kNm

The maximum stress caused by bending was then calculated by eq. 8 to;

� = 7.45 �� (24)

The design value of the bending strength was determined by eq. 11 to;

�, = 15,70 �� (25)

45 By comparing the result of the stresses caused by bending in eq. 24 with the design value of the bending strength, eq. 25 it can be seen that:

� < �, OK!

The stress caused by bending is lesser than the design bending strength of the material. Fracture will not occur.

The maximum shear stress was determined by eq. 9 and calculated to;

� = 0.67 �� (26)

The design value of the shear strength was determined by eq. 12 to;

� = 2.28 �� (27)

By comparing the result of the shear stresses in eq. 26 with the design value of the shear stress in eq. 27 it can be seen that;

� < � OK!

The shear stress is smaller than the allowed design value of shear stress. Fracture will not occur.

4.3.2 Calculations in SLS

Calculations in SLS were made regarding the instant deflection and the final deflection of the beam. This was done by using eq. 13 and eq. 15-18.

�, = 10.2 �� (28)

�, = 25.3 �� (29)

46 The maximum allowed deflection is given in eq. 19 and 20 and was calculated to;

�, = 21.25 �� (30)

�, = 28.3 �� (31)

By comparing the result from eq. 28 with eq. 30 and eq. 29 with eq. 31 it can be seen that;

�, < �, OK!

The deflection of the beam is within the allowed values of deflection.

The calculations regarding bending strength, shear strength and deflection show that the three steel beams in the case, illustrated in Figure 11, can be replaced with two glulam beams with the dimensions of 215x594 mm.

47 4.3.3 Service life

The expected service life of the reference case was calculated by using eq. 1-6. The service life model was only applied on the glulam beams that are supposed to replace the steel beams. The required service life of the structure in this case was set to 50 years according to the designer Ramboll Sweden AB. The influencing factors were determined and are presented below.

• Calibration factor is constant, � = 1.4 • Figure 8 and Table 5 shows the annual exposure dose. In the area where Lysekil is

located � = 43 • Figure 9 shows that the current area has a frequency of free driving rain index around 2.20 which is > 1.6. Free driving rain should therefore be considered. No shelter or protection against free driving rain is present which, according to Table 6, would give

a severe exposure corresponding to � = 1.0 • The deck in the specific case is not watertight and is not assumed to be considered as a shelter. Therefore, the load bearing beam is considered freely exposed to precipitation

with no shelter, � = 1.0 • The beams rest upon piles, but splashing from the piles is not considered to induce a higher moisture content. Therefore � is the closest distance to ground. The closest

distance to the ground, or in this case to the sea is � > 400 �� thus � = 1.0 • Wooden studs rest upon the glulam beams creating horizontal contact areas. The horizontal contact areas will trap water and thus have an increased moisture content

resulting in a “fair” exposure class, � = 1,5

By eq. 2 � can be calculated to be;

� = 90.3

For the specific case, a high severity class is required of the load bearing beams, which results in � = 1.0. The lamellae in the glulam beam will be individually pressure impregnated in the highest possible class, NTR-A. After the lamellae have been glued together, the beam is planed and will lose its impregnation class. The glulam beam will therefore have an

48 impregnation class corresponding to NTR-AB. NTR-AB will result in � = 1700. By inserting the selected factors to eq. 1, the expected service life can be calculated to;

�� = 19 �� < ��

By comparing the expected service life with the required service life, it can be seen that the expected service life is much shorter than the required one. Current design of the timber structure will not fulfil the requirements.

49 5 Discussion

This thesis aims to address the question of whether glulam could be a possible material to use in a marine environment. Furthermore, it discusses whether glulam beams can replace steel for use as load bearing elements in large jetties and small bridges situated in a marine environment. The question was addressed regarding durability, strength and service life, by applying findings on a real case and making calculations.

5.1 Literature study

The result from the literature study showed that glulam beams can be used in a marine environment. The content of salt in the water does not influence the properties or the degrading of the timber [9]. Regarding timber, saltwater has one disadvantage in comparison to fresh water, which is marine boring animals. For Swedish conditions, they are represented by shipworms. Shipworms attack below the water line and degrade timber severely in a short period of time [3, 5]. However, for structures situated above sea level, shipworms are not a concern. Since the salinity of the water does not influence the degrading of the material but rather acts as a wood preservative, timber used in a marine environment will not differ from similar constructions placed in close proximity to fresh water [9, 10]. The largest impact that marine environment has is the high moisture level it exposes the construction to. Not only does the construction have to withstand rain, but also splashing and spraying from the sea, which raises wood moisture content further.

The biggest problem that arises in this moisture rich environment is the possibility of rot. If the wood moisture content is higher than the critical value of 20%, the risk of rot occurring increases [1, 24]. Glulam and the environment discussed in this thesis will periodically have a moisture content above the critical value.

To protect the wood, glulam will need to be pressure impregnated to increase the service life of the structure. A higher impregnation class will lead to better protection against rot which results in a longer service life [1, 3]. For constructions placed in salt water, an impregnation class of NTR-M is recommended [1]. NTR-M is highly effective against rot, but also as protection against marine boring animals. All approved wood preservatives in class NTR-M are in the Nordic countries approved by the Nordic Wood Preservative Council and contain

50 creosote [13]. Creosote is not approved for use in the construction of jetties and small bridges, and thus the highest possible impregnation class for these types of structures is NTR-A [17]. For the wooden structure to be useable in a marine environment, it is imperative that the wood is not placed below the surface where marine boring animals can attack. Hence, the tidal cycles of the sea need to be taken into consideration to ensure that the timber element does not end up under water.

According to the definition of use classes and the NTR system seen in Table 1, the investigated structural elements were classified as UC3. That is what the placement of the elements above the ground and local environment call for. UC3 corresponds to the impregnation class NTR-AB [1, 9].

5.2 On the market

Durability by design is always necessary to prevent high moisture content in the wood, and together with pressure impregnation, wood protection can be increased significantly [1]. Preservative treatment is not an alternative method to a good design to prevent moisture in wood, but by pressure impregnating the material, the lifetime of the timber will increase. As has been mentioned earlier, glulam cannot be classified according to the NTR-system [18, 22]. This does not mean that pressure impregnated beams lack protection against fungal decay.

To be able to predict the expected service life, a corresponding NTR grading was necessary. NTR-B is defined by an impregnation depth of a few millimeters (see Table 1). In other words, the element is not fully impregnated in NTR-B. Diffusion of impregnant into a whole beam of glulam is limited due to the adhesive seam that joins the lamellae, as they are glued together before impregnation. Because of this, glulam beams impregnated after gluing were assumed to be limited to NTR-B.

Lamellae that are impregnated individually to NTR-A, and are glued together into beams after impregnation, were assumed to be of impregnation class corresponding to NTR-AB. This is because they are planed after gluing, which results in removal of the outermost layer of the wood and hence loss of impregnation class NTR-A. The beams are still fully impregnated, but not with the same amount of preservatives as before planing.

Impregnation class NTR-AB is defined as being fully impregnated, but not with an amount of impregnant as high as NTR-A (see Table 1). As previously mentioned, NTR-B means that only a few millimeters of the wood contain preservative. Because of this, beams with lamellae graded to NTR-AB before being glued together were not assumed to be of class NTR-B after planing as they are still fully impregnated. This is why the beams from Moelven Töreboda AB were not assumed to be of any corresponding impregnation class. Definition of a corresponding impregnation class was of importance for service life model calculations.

The purpose of the analysis of the market was to see what dimensions and preservative treatments are available in Sweden. Both Martinson Group AB and Moelven Töreboda AB could provide suitable dimensions for the structure in the case study. However, Martinson Group AB have the highest impregnation class on their products, corresponding to NTR-AB. Therefore, their products were most suitable for the calculations in the case study.

5.3 Case study

The case study was done to be able to apply the findings in the literature study on a real case and to see if there was a possibility of replacing the current steel beam in the structure with glulam beams. This was done by calculation in ULS and SLS and by prediction of expected service life. The high moisture content in the beam is important to take into consideration since it influences the strength and stiffness. The high moisture content also has a great impact on the creep and final deflection of the glulam beam [3, 5]. The high moisture content and its influence on the properties of the material was accounted for in the calculations by introducing selected material and load parameters. The calculations done in the case study showed that the glulam beams could replace current steel beams in the structure. The bending strength, shear strength, instant deflection and final deflection influenced by creep were determined for the glulam beams. The final deflection of the beam was the dimensioning parameter. Taking into account the dimensions available from Martinson Group AB, the suitable dimensions of the glulam beam were calculated to 215x594 mm. The three steel beams in the pedestrian jetty from the case study, seen in Figure 11-13, can be replaced with two glulam beams with the dimensions of 215x594 mm.

The expected service life was also determined for the specific case by the method presented in chapter 3.7. The evaluation of the expected service life showed that by simply replacing the current steel beams with glulam beams, the requirements for service life would not be met. The required service life was set to a minimum of 50 years and the expected service life was calculated to be 19 years. One of the issues with the structure considered in the case study was its geographic location. The annual exposure dose was shown to be higher in the area where the jetty is located than the rest of the Swedish coast [2]. The high exposure dose of precipitation, temperature, moisture and free driving rain in the area around Lysekil resulted in a short expected service life. For a jetty with a structure made entirely from wood in the current location and environment to last, a different design of the structure is needed to increase the service life.

When designing an intended timber structure, the guidelines to evaluate the expected service life are good to use. If the expected service life does not meet the requirements, improvements of the design can be made by adjusting the design and hence the factors k1, k2, k3, k4 and DRd. These factors correspond to protection from driving rain, sheltering from vertical rain, distance from ground, protection of end grain and preventing trapped or standing water [2]. Adjustments should be done with attention to detail and with an appropriate choice of material. In this specific case, improvements of the design with glulam beams can be made.

For instance, a watertight deck would shelter the beams from precipitation and reduce kE2 = 0.8. This would increase the expected service with a few years. Improved protection from driving rain can also be an alternative approach to extend the expected service life of the beams. The material chosen for the beams and its impregnation also have a great influence on service life. The same structure with an impregnation class of NTR-A shows increased service life by 10 years. However, glulam beams cannot obtain a corresponding impregnation class higher than NTR-AB using the impregnation methods and grading systems of today.

The method of determining the expected service life is arbitrary and developed for bridges. However, it was considered to give an accurate evaluation of the service life of the pedestrian jetty from the case study. Some factors were hard to determine, since the definition did not quite match the case. For example, since the deck of the case was not watertight, the overhang and sheltering from above could not be considered. The beam was therefore assumed to be

53 freely exposed to the rain with no shelter. Even though the deck is not watertight, it will provide some protection from rain.

For the purposes of calculation, the service life is assumed to be finished when rot occurs. Rot will eventually occur where the moisture content is above the critical value of 20% [1, 24]. A high moisture content can occur in the whole element or it can occur locally. Horizontal surfaces, moisture traps and end grain are details that need to be considered in this context, which is why the design of the structure is important [2, 9]. In this case, studs will rest upon the glulam beams and create horizontal contact areas between the surfaces. This will increase the moisture content at these points. As discussed, the deck is not watertight and cannot be assumed to provide shelter for these contact areas. With a watertight deck, the risk of high moisture content on the horizontal surface of the glulam beam and the contact areas with the studs will be reduced.

The service life is hard to predict. There is no quantitative method to evaluate the service life or the degrading process of timber. The guidelines for evaluating the expected service life that have been established by Pousette et al [2] are meant for risk assessment of intended bridge structures or similar structures. The model is not complete and more work needs to be done to develop a standardized method to evaluate the service life of timber structures. According to Pousette et al [2], the model has some uncertainties regarding the bridges treated with preservatives. The model has been verified from investigations of real bridges, but there was a lack of information about the quality of the treatment used on the pressure impregnated bridges they studied. This creates uncertainties. More bridges should be examined to verify the model with greater certainty, especially in the case of pressure impregnated timber bridges. Nevertheless, this method provides a good reference for what service life that can be expected for timber structures. It is therefore good to use when designing new bridges or similar constructions such as jetties.

54 6 Conclusions

The question if glulam beams can be used as load bearing elements for jetties and small bridges in a marine environment was answered, and the goals of this thesis were reached. The question has been evaluated regarding durability, what is on the market, strength and service life. The possibilities of using strength-classified glulam with pressure impregnation in a marine environment were investigated and evaluated. The findings were applied to perform calculations on a specific case, and expected service life was estimated. The result was as follows.

The marine environment does not bring with it any other disadvantages than the environment in close proximity to fresh water does. The salinity of the marine environment does not have a negative effect on the timber, but rather acts as a wood preservative. The only demand is that the structure needs to be placed above the sea level.

The highest possible impregnation class for this type of construction in Sweden is NTR-A. Glulam is per definition not classifiable in the NTR system. To be able to estimate the service life of the glulam beam, a corresponding impregnation class has to be identified. Glulam cannot reach a higher corresponding impregnation class than NTR-AB.

From the analysis of the glulam market in Sweden, it was concluded that Martinson Group AB are able to provide material of the highest possible corresponding impregnation class. Beams of the dimension required in this construction can also be provided by Martinson Group AB.

The calculations of beam strength and deflection show that in this case glulam beams have adequate strength to bear the load of the construction. When it comes to deflection, glulam shows creep over time, especially in a moisture rich environment. In this case, the deflection over time was the dimensioning value for the beam dimensions chosen for this construction.

Regarding service life, the model used for calculation is based on environmental factors and moisture exposure of the material. In this case the glulam beam does not meet the specified service life requirements for the construction. This problem can possibly be solved by modifying design in order to provide better moisture protection for the beam.

55 In conclusion, glulam beams can be an alternative material to use in marine environments if they are placed above sea level. The current design of the structure in the case of this thesis is not suitable for glulam beams since the design does not provide sufficient service life of the glulam elements. For possible use of glulam beams in structures such as jetties and small bridges, a proper design providing moisture protection and appropriate impregnation of the material is crucial. If these parameters are fulfilled, glulam is a valid alternative material for use in marine environment.

56 7 References

[1] Swedish Wood, [Online]. Available: https://www.svenskttra.se. [Accessed 28 01 2020].

[2] A. Pousette, K. Malo, S. Thelandersson, S. Fortino, L. Salokangas and J. Wacker, "Durable Timber Bridges Final Report and Guidlines," RISE, Skellefteå, 2017.

[3] P. Domone and J. Illstone, "Timber," in Construction Materials. Their nature and behaviour., 2 Park Squere, Milton Park, Abingdon, Oxon, Spon Press, 2010, pp. 403-506.

[4] Swedish Wood, "Design of timber structures, volume 1," Swedish Fores Industries Federation, Stockholm, 2016.

[5] P. G. Burström, in Byggmaterial. Uppbyggnad, tillverkning och egenskaper, Lund, Studentlitteratur AB, 2007, pp. 363-394.

[6] Swedish institute for Standards, "SIS," [Online]. Available: https://www.sis.se/standarder/ce- markning/. [Accessed 14 02 2020].

[7] J. Niklewiski, "Durability of timber members. Moiture conditions and service life assessment of bridge detailing.," Lund Univeristy, Lund, Sweden, 2018.

[8] Svenskt Trä, "Träguiden," 06 08 2018. [Online]. Available: https://www.traguiden.se/om- tra/materialet-tra/traets-egenskaper-och-kvalitet/bestandighet1/mikroorganismer1/. [Accessed 14 04 2020].

[9] M. Crossman and J. Simm, Manual on the use of timber in coastal and river engineering, London: ICE Publishing, 2011.

[10] A. Treu, K. Zimmer, C. Brischke, E. Larnoy, L. R. Gobakken, F. Aloui, S. M. Cragg, P.-O. Flæte, M. Humar, M. Westin, L. Borges and J. Williams, "Durability and protection of timber structures in marine environments in Europe: An overview," Bio Resources, 11 10 2019.

[11] SIS Swedish standard, "SS-EN 335:2013, Durability of wood and wood-based products - Use classes: definitions, applications to solid wood and wood based products," 25 03 2013. [Online]. Available: https://www.sis.se. [Accessed 28 02 2020].

[12] Svenskt trä, "Träguiden," Svenskt trä, 20 08 2015. [Online]. Available: https://www.traguiden.se/om-tra/standard/bestandighet-och-traskydd/bestandighet-och- traskydd/biologiska-anvandningsklasser/. [Accessed 11 02 2020].

[13] Nordic Wood Preservative Council, "Nordiska träskyddsrådet," 01 01 2020. [Online]. Available: https://www.ntr-nwpc.com/godkannanden-2/ntr-godkanda-traskyddsmedel. [Accessed 31 01 2020].

[14] NTR Nordiska träskyddsrådet, "NWPC Document No 1:2017," 01 01 2017. [Online]. Available: https://assets.website- files.com/5be551a010d5ce592ab25722/5bf2cbaa60911a6510565164_NTR%20Doc%201%20p art%201%20(2).pdf. [Accessed 18 02 2020].

57 [15] E. Salminen, M. Korhonen and R. Jernlås, "Wood Preservation with chemicals," Nordic Council of Minister, Copenhagen, 2014.

[16] Kemikalieinspektionen, "KEMI," 02 2018. [Online]. Available: https://www.kemi.se/global/faktablad/faktablad-om-impregnerat-virke.pdf. [Accessed 10 02 2020].

[17] Trafikverket, "Krav Brobyggande TDOK 2016:0204," 05 06 2019. [Online]. Available: https://trafikverket.ineko.se/Files/sv-SE/10753/RelatedFiles/2011_085_trvk_bro_11.pdf. [Accessed 11 02 2020].

[18] Svenskt Trä, Limträhandbok Del 2, Stockholm: Föreningen Sveriges Skogsindustri, 2016.

[19] SIS Swedish standard, "SS-EN 14080:2013, Timber structures-Glued laminated timber and glued solid timber-Requirements," 01 07 2013. [Online]. Available: https://www.sis.se. [Accessed 18 02 2020].

[20] Svenskt Trä, "Träguiden," 15 08 2017. [Online]. Available: https://www.traguiden.se/om- tra/materialet-tra/trabaserade-produkter/konstruktionselement1/limtra/. [Accessed 17 04 2020].

[21] Svensk trä, "Hållfasthetsklasser för limträ," 08 2015. [Online]. Available: https://www.svenskttra.se/siteassets/6-om-oss/publikationer/pdfer/hallfasthetsklasser- for_limtra.pdf. [Accessed 18 02 2020].

[22] Svenkt Trä, "Träguiden," 18 01 2017. [Online]. Available: https://www.traguiden.se/konstruktion/limtrakonstruktioner/fakta-om- limtra/projektering/traskydd/impregnerat-limtra/. [Accessed 31 01 2020].

[23] A. Pousette and P.-A. Fjellström, "Experiance from timber bridges inspections in Sweden - Examples of influence of moisture," SP Sveriges Tekniska Forskningsintitut, Borås, 2016.

[24] SIS Swedish standard, "SS-EN 1995-1-1:2004, Eurocode 5: Design of timber structures - Part 1-1: General-Common rules and rules for buildings," 10 12 2004. [Online]. Available: https://www.sis.se. [Accessed 18 02 2020].

[25] SIS Swedish Standard, "SS-EN 1991-1-1 Eurocode 1: Actions on structures," 2011-01-26. [Online].

[26] SIS Swedish Standard, "SS-EN 1995-2:2004 Eurocode 5: Design of timber structures - Bridges," 13 10 2009. [Online].

[27] SIS Swedish Standard, "SS-EN 1990 Eurocode - Basis of structural design," 28 06 2002. [Online].

[28] Boverket, "Boverkets konstruktionsregler EKS 11," 05 2019. [Online]. Available: https://www.boverket.se/globalassets/publikationer/dokument/2019/eks-11.pdf. [Accessed 06 06 2020].

[29] Svenskt Trä, Dimensionering av Träkonstruktioner - Del 1, Stockholm: Föreningen Sveriges Skogsindustrier, 2019.

58 [30] Transportstyrelsen, "TSFS 2018:57 Transportstyrelsens föreskrifter och allmänna råd om tillämpning av eurokoder," 01 11 2018. [Online].

[31] SIS Swedish Standard, "Eurocode 1: Actions on structures - Part 1-1: Genral actions - Densities, sef-weight, imposed loads for buildings," [Online].

[32] Swedish Wood, Design of Timber Structures - volume 1, Stockholm: Swedish Forest Industries Federation, 2016.

59 Appendix A