Seismic Design Provisions of BNBC-2020: Part 2

S. K. Ghosh Associates LLC International Code Council (ICC)

Date: 26 May 2021

Dr. S. K. Ghosh President, S. K. Ghosh Associates LLC

URP S-09 Training Module S5

PART 5 EQUIVALENT LATERAL FORCE PROCEDURE

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ASCE 7-05 12.8.6, 2.5.7.7 Story Drift Determination (')

Lateral displacement of one level relative to the next level above or below

Analysis of Structures under Code- Prescribed Seismic Forces

G QE xe

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ASCE 7-05 12.8.6, 2.5.7.7 Story Drift Determination (')

'x = Gx - Gx-1 'a where….

Gx = Cd Gxe / I

ASCE 7-05 12.8.6, 2.5.7.7 Story Drift Determination (')

Cd = displacement amplification factor (ASCE 7-05 Table 12.2-1, Table 6.2.19)

Gxe = elastic analysis displacement

'a = allowable story drift (ASCE 7-05 Table 12.12-1, Table 6.2.21, Section 2.5.14)

I = seismic importance factor (ASCE 7-05 Table 1.5-2, Table 6.2.17)

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Allowable Story Drift ('a ) ASCE 7-05 Table 12.12-1, Table 6.2.21

Occupancy Category Building I or II III IV Buildings 4 stories in height; other than masonry; 0.025h 0.020h 0.015h Non-structural elements designed to sx sx sx accommodate story drift Masonry cantilever shear wall 0.010h 0.010h 0.010h buildings sx sx sx Other masonry shear walls buildings 0.007hsx 0.007hsx 0.007hsx All other buildings 0.020hsx 0.015hsx 0.010hsx

ݔ = Story height below levelݏ

2.5.14.1 Story Drift Limit

For seismic force–resisting systems comprised solely of moment frames in Seismic Design Categories D, the allowable storey drift for such linear elastic analysis procedures shall not exceed ǻ / where is termed as a structural redundancy factor. The value of redundancy factor may be considered as 1.0 with exception of structures of very low level of redundancy where may be considered as 1.3. For nonlinear time history analysis (NTHA), the storey drift obtained (Sec 2.5.11) shall not exceed 1.25 times the storey drift limit specified above for linear elastic analysis procedures.

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2.5.14.3 Separation between adjacent structures

Buildings shall be protected from earthquake-induced pounding from adjacent structures or between structurally independent units of the same building maintaining safe distance between such structures as follows:

(i) for buildings, or structurally independent units, that do not belong to the same property, the distance from the property line to the potential points of impact shall not be less than the computed maximum horizontal displacement (Sec 2.5.7.7) of the building at the corresponding level.

(ii) for buildings, or structurally independent units, belonging to the same property, if the distance between them is not less than the square root of the sum- of the squares (SRSS) of the computed maximum horizontal displacements (Sec 2.5.7.7) of the two buildings or units at the corresponding level.

(iii) if the floor elevations of the building or independent unit under design are the same as those of the adjacent building or unit, the above referred minimum distance may be reduced by a factor of 0.7

2.5.14.4 Special Deformation Requirement for Seismic Design Category D [Deformation Compatibility] For structures assigned to SDC D, every structural component not included in the seismic force–resisting system in the direction under consideration shall be designed to be adequate for the gravity load effects and the seismic forces resulting from displacement to the design story drift (ǻ) as determined in accordance with Sec 2.5.7.7. Even where elements of the structure are not intended to resist seismic forces, their protection may be important. Where determining the moments and shears induced in components that are not included in the seismic force– resisting system in the direction under consideration, the stiffening effects of adjoining rigid structural and nonstructural elements shall be considered and a rational value of member and restraint stiffness shall be used.

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2.5.14.3 Separation between adjacent structures

PART 6 EARTHQUAKE LOAD EFFECTS AND LOAD COMBINATIONS

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2.7.3 Strength Design Load Combinations

1. 1.4(D + F)

2. 1.2(D + F + T) + 1.6(L + H) + 0.5(Lr or R)

3. 1.2D + 1.6(Lr or R) + (L or 0.8W)

4. 1.2D + 1.6W + L + 0.5(Lr or R) 5. 1.2D + 1.0E + 1.0L 6. 0.9D + 1.6W + 1.6H 7. 0.9D + 1.0E + 1.6H

2.7.3 Strength Design Load Combinations (without F, H, T)

1. 1.4D

2. 1.2D + 1.6L + 0.5(Lr or R)

3. 1.2D + 1.6(Lr or R) + (L or 0.8W)

4. 1.2D + 1.6W + L + 0.5(Lr or R) 5. 1.2D + 1.0E + 1.0L 6. 0.9D + 1.6W 7. 0.9D + 1.0E

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Seismic Strength Design Load Combinations

1.2D + 1.0E + 1.0L

0.9D + 1.0E

E = UQE + 0.2SDSD ASCE 7-05 12.4.2

E = UQE -0.2SDSD ASCE 7-05 12.4.2

U = 1 in Seismic Design Category (SDC) A, B, and C

U = 1 or 1.3 in SDC D, E, and F

2.5.13 Earthquake Load Effects and Load Combinations In BNBC-2020 U = 1 (not mentioned at all) = (6.2.56) = = =

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Effect of Vertical Earthquake Ground Motion Gravity and Earthquake Effects Additive = = = Dhaka, Zone-2, Soil Type SD: = 0.45 =

The load factor on live load L in combinations (3), (4), and (5) is permitted to be reduced to 0.5 for all occupancies in which minimum specified uniformly distributed live load is less than or equal to 5.0 kN/m2, with the exception of garages or areas occupied as places of public assembly.

Effect of Vertical Earthquake Ground Motion Gravity and Earthquake Effects Counteractive = = = Dhaka, Zone-2, Soil Type SD: = 0.45 =

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Load Combinations with Overstrength Factor

Cantilever Column Systems ASCE 7-05 12.2.5.2 SDC B-F Foundation and other elements used to provide overturning resistance at the base of cantilever column elements shall have the strength to resist the load combinations with over strength factor of Section 12.4.3.2.

Load Combinations with Overstrength Factor

Elements Supporting ASCE 7-05 12.3.3.3 Discontinuous Walls or Frames SDC B-F

SHEAR WALL

Elements supporting discontinuous walls or frames

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Load Combinations with Overstrength Factor

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Load Combinations with Overstrength Factor

Collector Elements ASCE 7-05 12.10.2.1 (SDC C-F)

Load Combinations with Overstrength Factor

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2.5.13.4 Load Combinations with Overstrength Factor Basic Combinations for Strength Design with Overstrength Factor

(1.2 + 0.2SDS)D + :0QE + L

(0.9 í 0.2SDS)D + :0QE

2.5.5.6 Provisions for Using System Overstrength Factor, ȍo

2.5.5.6.1 Combinations of Elements Supporting Discontinuous Walls or Frames. Columns, beams, trusses, or slabs supporting discontinuous walls or frames of structures having horizontal irregularity Type IV of Table 6.1.5 or vertical irregularity Type IV of Table 6.1.4 shall have the design strength to resist the maximum axial force that can develop in accordance with the load combinations with overstrength factor of Section 2.5.13.4. The connections of such discontinuous elements to the supporting members shall be adequate to transmit the forces for which the discontinuous elements were required to be designed.

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2.5.5.6 Provisions for Using System Overstrength Factor, ȍo

2.5.5.6.2 Increase in Forces Due to Irregularities for Seismic Design Categories D through E.

For structures assigned to Seismic Design Category D or E and having a horizontal structural irregularity of Type I.a, I.b, II, III, or IV in Table 6.1.5 or a vertical structural irregularity of Type IV in Table 6.1.4, the design forces determined from Section 2.5.7 shall be increased 25 percent for connections of diaphragms to vertical elements 6-104 Vol. 2 and to collectors and for connections of collectors to the vertical elements. Collectors and their connections also shall be designed for these increased forces unless they are designed for the load combinations with overstrength factor of Section 2.5.5.4, in accordance with Section 2.5.13.4.

2.5.5.6 Provisions for Using System Overstrength Factor, ȍo 2.5.5.6.3 Collector Elements Requiring Load Combinations with Overstrength Factor for Seismic Design Categories C through E. In structures assigned to Seismic Design Category C, D or E, collector elements, splices, and their connections to resisting elements shall resist the load combinations with overstrength of Section 2.5.13.4.

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2.5.5.6 Provisions for Using System Overstrength Factor, ȍo

2.5.5.6.4 Batter Piles. Batter piles and their connections shall be capable of resisting forces and moments from the load combinations with overstrength factor of Section 2.5.13.4. Where vertical and batter piles act jointly to resist foundation forces as a group, these forces shall be distributed to the individual piles in accordance with their relative horizontal and vertical rigidities and the geometric distribution of the piles within the group.

PART 3 BUILDING CONFIGURATION

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Building Configuration

Horizontal Irregularities (ASCE 7-05 Table 12.3-1) 1a. Torsional irregularity 1b. Extreme torsional irregularity 2. Re-entrant corners 3. Diaphragm discontinuity 4. Out-of-plane offsets 5. Nonparallel systems

2.5.5.3 Building Irregularity

2.5.5.3.1 Plan irregularity: Following are the different types of irregularities that may exist in the plan of a building.

(i) Torsion irregularity

(To be considered for rigid floor diaphragms, when the maximum storey drift (ǻ݉ܽݔ as shown in Figure 6.2.27(a), computed including accidental torsion, at one end

of the structure is more than 1.2 times the average [ǻܽݒ݃=(ǻ݉ܽݔ+ǻ݉݅݊)/2] of the story drifts at the two ends of the structure. If ǻ݉ܽݔ>1.4ǻܽݒ݃ then the irregularity is termed as extreme torsional irregularity.

(ii) Re-entrant corners

Both projections of the structure beyond a re-entrant comer [Figure 6.2.27(b)] are greater than 15 percent of its plan dimension in the given direction.

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2.5.5.3.1 Plan Irregularity

(iii) Diaphragm Discontinuity

Diaphragms with abrupt discontinuities or variations in stiffness, including those having cut-out [Figure 6.2.27(c)] or open areas greater than 50 percent of the gross enclosed diaphragm area, or changes in effective diaphragm stiffness of more than 50 percent from one story to the next.

(iv) Out- of-Plane Offsets

Discontinuities in a lateral force resistance path, such as out of-plane offsets of vertical elements, as shown in Figure 6.2.27(d).

(v) Non-parallel Systems

The vertical elements resisting the lateral force are not parallel to or symmetric [Figure 6.2.27(e)] about the major orthogonal axes of the lateral force resisting elements.

Building Configuration

Vertical Irregularities (ASCE 7-05 Table 12.3-2) 1a. Stiffness irregularity – soft story 1b. Extreme soft story 2. Weight (mass) irregularity 3. Vertical geometric irregularity 4. In-plane discontinuity in vertical lateral-force-resisting elements 5a. Discontinuity in lateral strength – weak story 5b. Extreme weak story

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2.5.5.3 Building Irregularity

2.5.5.3.2 Vertical Irregularity: Following are different types of irregularities that may exist along vertical elevations of a building.

(i) Stiffness Irregularity - Soft Storey

A soft storey is one in which the lateral stiffness is less than 70% of that in the storey above or less than 80% of the average lateral stiffness of the three storeys above irregularity [Figure 6.2.28(a)]. An extreme soft storey is defined where its lateral stiffness is less than 60% of that in the storey above or less than 70% of the average lateral stiffness of the three storeys above.

(ii) Mass Irregularity

The seismic weight of any storey is more than twice of that of its adjacent storeys [Figure 6.2.28(b)]. This irregularity need not be considered in case of roofs.

2.5.5.3.2 Vertical Irregularity

(iii) Vertical Geometric Irregularity

This irregularity exists for buildings with setbacks with dimensions given in Figure 6.2.28(c). [Different from ASCE 7-05]

(iv) Vertical In-Plane Discontinuity in Vertical Elements Resisting Lateral Force

An in-plane offset of the lateral force resisting elements greater than the length of those elements Figure 6.2.28(d). [Different from ASCE 7-05]

(v) Discontinuity in Capacity - Weak Story

A weak story is one in which the story lateral strength is less than 80% of that in the story above. The story lateral strength is the total strength of all seismic force resisting elements sharing the story shear in the considered direction [Figure 6.2.28(e)]. An extreme weak story is one where the storey lateral strength is less than 65% of that in the story above.

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Road Map

Earthquake experiences with irregular structures

Horizontal structural irregularities

Vertical structural irregularities

Configuration

Relative arrangement of parts; something produced by such arrangement.

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Structural Configuration

Horizontal (Plan) Configuration Vertical Configuration

Photo Credit: EERI Earthquake Damage Slide Set

Structural Configuration and Seismic Performance The configuration of a structure can significantly affect its performance during a strong earthquake that produces the ground motion contemplated in the IBC/ASCE 7.

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Structural Configuration and Seismic Performance IBC/ASCE 7 seismic design provisions were developed basically for regular buildings. Past earthquakes have repeatedly shown that irregular buildings suffer greater damage than regular buildings. This happens even with good design and construction.

Earthquake Experience

Magnitude 7.1 Loma Prieta, CA October 17, 1989

Three and four story wood frame, brick veneer buildings in the Marina District of San Francisco sustained damage as a consequence of the ground shaking (10%g at rock sites, 20 to 30%g on sites underlain by bay mud) and liquefaction. The soft first story made the buildings more vulnerable. Buildings at corners of blocks sustained heavier damage than those within the block.

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Earthquake Experience

Photo Credit: EERI Earthquake Damage Slide Set

Earthquake Experience

Marina District…a “stiffness” issue (SOFT STORY)

Photo Credit: EERI Earthquake Damage Slide Set

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Earthquake Experience

Magnitude 6.5 San Fernando, CA February 9, 1971

Failure of columns of “SOFT STORY” Olive View Hospital. The failure of the canopy pinned the ambulances, rendering them useless. Ground shaking is estimated to have reached approximately 100%g at the site.

Earthquake Experience

Photo Credit: EERI Earthquake Damage Slide Set

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Earthquake Experience

Magnitude 7.9 Philippines August 16, 1976

Damage to reinforced concrete building. Torsion (or twisting) of structures is a common cause of failure when the centers of mass and stiffness are different. Buildings at corners of blocks are often more vulnerable than those within the block because two sides are open (e.g. glass windows for advertising) and two sides are solid (e.g. at property lines). The first floor has pancaked.

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Earthquake Experience

Photo Credit: EERI Earthquake Damage Slide Set

Earthquake Experience

Magnitude 8.0 Mexico City Sept. 19, 1985 Triangular structures(“flat iron” buildings) created because the streets are not at right angles with each other are even more vulnerable than square buildings at corners of blocks.

These buildings have only one Photo Credit: EERI Earthquake Damage Slide Set solid and two glass walls. Note the torsional distress.

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Reasons for Poor Seismic Performance of Irregular Structures In a regular structure, inelastic demands produced by strong ground shaking tend to be well distributed throughout the structure, resulting in a dispersion of energy dissipation and damage. In irregular structures, inelastic behavior can concentrate in the zone of irregularity, resulting in rapid failure of structural elements in these areas.

Reasons for Poor Seismic Performance of Irregular Structures Some irregularities introduce unanticipated stresses into the structure, which designers frequently overlook when detailing the structural system.

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Reasons for Poor Seismic Performance of Irregular Structures Elastic analysis methods typically employed in structural design often cannot predict the distribution of earthquake demands in an irregular structure very well, leading to inadequate design in the zone of irregularity.

Code Regulations Concerning Irregular Structures Introduced in the 1988 Uniform Building Code (UBC). Evolved since then. Thrust is to encourage that buildings be designed to have regular configurations. Important feature is prohibition of gross irregularity in buildings located on sites close to major faults, where very strong ground motion and extreme inelastic demands can be experienced (mostly not a consideration in Bangladesh).

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Horizontal Irregularities (ASCE 7-05 Table 12.3-1) 1a. Torsional 1b. Extreme torsional (2000 IBC) 2. Reentrant corner 3. Diaphragm discontinuity 4. Out-of-plane offset 5. Nonparallel system

Vertical Irregularities (ASCE 7-05 Table 12.3-2) 1a. Stiffness-soft story 1b. Stiffness-extreme soft story (2000 IBC) 2. Weight (mass) 3. Vertical geometric 4. In-plane discontinuity in vertical lateral force- resisting element 5a. Discontinuity in lateral strength – weak story 5b. Discontinuity in lateral strength – extreme weak story (ASCE 7-05/2006 IBC)

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Seismic Design CodeMaster

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Seismic Analysis Procedure Selection

ASCE 7-05 STATIC ANALYSIS PROCEDURES SECTION Simplified Design Procedure (not in 12.14 BNBC) Equivalent Lateral Force Procedure 12.8 2.5.7

Seismic Analysis Procedure Selection ASCE 7-05 DYNAMIC ANALYSIS PROCEDURES SECTION Modal Response Spectrum Analysis 12.9 2.5.9

Linear Response History Analysis 16.1 2.5.10

Nonlinear Response History Analysis 16.2 2.5.11

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Table 12.6-1 Permitted Analytical Procedures

Seismic Analysis Procedure Selection, Table 12.6-1

If a building is assigned SDC D, E, or F and has a

T 3.5 Ts, then dynamic analysis procedure must be used.

SD1 Ts = SDS

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Horizontal Irregularities (Table 12.3-1), 2.5.5.3.1 1a. Torsional 1b. Extreme torsional 2. Reentrant corner 3. Diaphragm discontinuity 4. Out-of-plane offset Whittier Earthquake Oct 1, 1987 5. Nonparallel system Magnitude 5.1

Horizontal Irregularities (Table 12.3-1), 2.5.5.3.1

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Part 6, Chapter 1,Table 6.1.5 Horizontal Structural Irregularities (Essentially Repeated in 2.5.5.3.1)

Part 6, Chapter 1, 1.7.3.8 Floor and roof diaphragms

(d) Structures having irregularities

(i) For structures assigned to Seismic Design Category D and having a plan irregularity of Type I, II, III, or IV in Table 6.1.5 or a vertical structural irregularity of Type IV in Table 6.1.4, the design forces determined from Sec 2.5.7 shall be increased 25 percent for connections of diaphragms to vertical elements and to collectors and for connections of collectors to the vertical elements. Collectors and their connections also shall be designed for these increased forces unless they are designed for the load combinations with over strength factor. [Also required by 2.5.5.6.2].

(ii) For structures having a plan irregularity of Type II in Table 6.1.5, diaphragm chords and collectors shall be designed considering independent movement of any projecting wings of the structure. Each of these diaphragm elements shall be designed for the more severe of the following cases:

Motion of the projecting wings in the same direction.

Motion of the projecting wings in opposing directions.

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ASCE 7-05 Table 12.3-1, 2.5.5.3.1(i) Torsional Irregularities

Gavg

Gmax

Gmax 1.2Gavg ------No irregularity

1.2Gavg < Gmax 1.4Gavg ------Irregularity

Gmax > 1.4Gavg ------Extreme Irregularity

Calculation of Gmax, Gavg includes accidental torsion, with Ax = 1.0.

ASCE 7-05 Table 12.3-1, 2.5.5.3.1(i) Horizontal Irregularity 1a: Torsional Irregularity

Refer to ASCE 7-10 Table 12.3-1

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Horizontal Irregularity 1a: Torsional Irregularity

Section SDC Description 12.3.3.4 D-F 25% increase in seismic forces in connections 2.5.5.6.2 in diaphragms and collectors Table D-F Permitted analytical procedure 12.6.1 ELF Prohibited Not in BNBC-2020 12.7.3 B-F 3-D structural model required Not explicit in BNBC-2020 12.8.4.3 C-F Amplification of accidental torsion 2.5.7.6.2 12.12.1 C-F Design story drift based on largest difference in 2.5.14.1 deflection 16.2.2 B-F 3-D structural model required in nonlinear response history procedure Not explicit in BNBC-2020

Design Force Increase due to Irregularities

12.3.3.4 Increase in Forces Due to Irregularities for Seismic Design Categories D through F. For structures assigned to Seismic Design Category D, E, or F and having a horizontal structural irregularity of Type 1a, 1b, 2, 3, or 4 in Table 12.3-1 or a vertical structural irregularity of Type 4 in Table 12.3-2, the design forces determined from Section 12.10.1.1 shall be increased 25 percent for the following elements of the seismic force-resisting system:

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Design Force Increase due to Irregularities (cont.) 1. Connections of diaphragms to vertical elements and to collectors. 2. Collectors and their connections, including connections to vertical elements of the seismic force-resisting system. EXCEPTION: Forces calculated using the seismic load effects including overstrength factor of Section 12.4.3 need not be increased.

Design Force Increase due to Irregularities

DIAPHRAGM

COLLECTOR DIAPHRAGM SHEAR

SHEAR WALL

A C B

OUT-OF-PLANE WALL SHEAR WALL (VERTICAL-RESISTING 2 ELEMENT) F

1 2

ISOMETRIC 1 FREE BODY DIAGRAM

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Design Force Increase due to Irregularities

BOUNDARY NAILING COLLECTOR STRAP

COLLECTOR 2X BLKG SHEAR WALL TRIMMER

KING STUD

DIAPHRAGM TO COLLECTOR CONNECTION A COLLECTOR TO VERTICAL ELEMENT (SHEAR WALL) CONNECTION B

BOUNDARY NAILING

DIAPHRAGM EDGE NAILING 2X BLKG

VERTICAL ELEMENT (SHEAR WALL)

DIAPHRAGM TO VERTICAL ELEMENT (SHEAR WALL) CONNECTION C

Permitted Analytical Procedures

Torsional modes of vibration may be excited, whose effects may not be adequately represented by the equivalent lateral force procedure.

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2.5.6 Static Analysis Procedure

This type of analysis may be applied to buildings whose seismic response is not significantly affected by contributions from modes higher than the fundamental mode in each direction. This requirement is deemed to be satisfied in buildings which fulfill the following two conditions: (a) The building period in the two main horizontal directions is smaller than both 4TC (TC is defined in Sec 2.5.4.3) and 2 seconds. (b) The building does not possess irregularity in elevation as defined in Sec 2.5.5.3.

12.8.4 Horizontal Distribution of Forces

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12.8.4 Horizontal Distribution of Forces Torsion • Torsional moment due to difference in location of center of mass and center of resistance • Must be considered for non-flexible diaphragms Accidental torsion • For non-flexible diaphragms, must be included in addition to the torsional moment • Displacement of center of mass = 5% building dimension perpendicular to direction of applied forces

12.8.4.3 Amplification of Torsion For structures assigned to SDC C, D, E, or F without flexible diaphragm and with horizontal irregularity Type 1a or 1b (Torsional Irregularity or Extreme Torsional Irregularity), the accidental torsion Mta at each floor level needs to be amplified by a factor:

2 § G · 0.1 d A ¨ max ¸ d 0.3 (12.8-14) x ¨ ¸ © 2.1 Gavg ¹

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Amplification of Torsion

ASCE 7-05 Figure 12.8-1

2.5.7.6.2 Accidental Torsional Effects

Where torsional irregularity exists (Sec 2.5.5.3.1) for Seismic Design Category C or D, the irregularity effects shall be accounted for by increasing the accidental torsion at each level by a torsional amplification factor, as illustrated in Figure 6.2.29 determined from the following equation: (6.2.44)

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Design story drift for Horizontal Irregularity Type 1a or 1b

12.8.6 Story Drift Limit. . . . For structures assigned to Seismic Design Category C, D, E, or F having horizontal irregularity Types 1a or 1b of Table 12.3-1, the design story drift, shall be computed as the largest difference of the deflections of vertically aligned points at the top and bottom of the story under consideration along any edges of the structure. [2.5.14.1]

Horizontal Irregularities (Table 12.3-1)

1a. Torsional 1b. Extreme torsional 2. Reentrant corner 3. Diaphragm discontinuity 4. Out-of-plane offset 5. Nonparallel system

Feb. 23, 2010 Chile Earthquake O’Higgins Building (23 stories) Conception

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Horizontal Irregularity 1b: Extreme Torsional Irregularity

Refer to ASCE 7-10 Table 12.3-1

Horizontal Irregularity 1b: Extreme Torsional Irregularity 12.3.3.1:PROHIBITED IN SDC E & F!!

Areas where S1 0.75g Do not exist in Bangladesh

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Horizontal Irregularity 1b: Extreme Torsional Irregularity Section SDC Description 12.3.3.4 D-F 25% increase in seismic forces in connections 2.5.5.6.2 in diaphragms and collectors Table D-F Permitted analytical procedure 12.6.1 ELF Prohibited Not in BNBC-2020 12.7.3 B-F 3-D structural model required Not explicit in BNBC-2020 12.8.4.3 C-F Amplification of accidental torsion 2.5.7.6.2 12.12.1 C-F Design story drift based on largest difference in 2.5.14.1 deflection 16.2.2 B-F 3-D structural model required in nonlinear response history procedure Not explicit in BNBC-2020

Horizontal Irregularity 2: Reentrant Corner Irregularity

Refer to ASCE 7-10 Table 12.3-1

RE-ENTRANT CORNER EXISTS WHEN PROJECTION b > 0.15a, AND PROJECTION d > 0.15c

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Horizontal Irregularity 2: Reentrant Corner Irregularity

Section SDC Description 12.3.3.4 D-F 25% increase in seismic forces in connections in 2.5.5.6.2 diaphragms and collectors Table D-F Permitted analytical procedure 12.6.1 ELF Permitted Also in BNBC-2020

Horizontal Irregularity 2: Reentrant Corner Irregularity Re-entrant corners may form coupled wings, which may respond in an opening and closing fashion. This may give rise to high stresses in the vicinity of re-entrant corners.

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Horizontal Irregularity 3: Diaphragm Discontinuity Irregularity

Refer to ASCE 7-10 Table 12.3-1

DIAPHRAGM DISCONTINUITY EXISTS WHEN AREA OF OPENING > 0.5ab OR EFFECTIVE DIAPHRAGM STIFFNESS CHANGES MORE THAN 50% FROM ONE STORY TO THE NEXT.

Horizontal Irregularity 3: Diaphragm Discontinuity Irregularity Section SDC Description 12.3.3.4 D-F 25% increase in seismic forces in connections in 2.5.5.6.2 diaphragms and collectors Table D-F Permitted analytical procedure 12.6.1 ELF Permitted Also in BNBC-2020

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Horizontal Irregularity 3: Diaphragm Discontinuity Irregularity

Q/A Horizontal Irregularity 3: Diaphragm Discontinuity Irregularity

Q. If the roof diaphragm has an opening in it which results in the stiffness of the 2nd floor diaphragm being 50 percent stiffer than the roof, does that make it irregular? The plan irregularity definition says story to story. A. Yes, it would be considered irregular...doesn't matter if floor or roof.

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Horizontal Irregularity 4: Out-of-Plane Offset Irregularity

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Horizontal Irregularity 4: Out-of-Plane Offset Irregularity

Section SDC Description 12.3.3.3 B-F Overstrength factor for elements supporting 2.5.5.6.1 discontinuous walls or frames 12.3.3.4 D-F 25% increase in seismic forces in connections in 2.5.5.6.2 diaphragms and collectors Table D-F Permitted analytical procedure 12.6.1 ELF Permitted Also in BNBC-2020 12.7.3 B-D 3-D structural model required Not explicit in BNBC-2020 16.2.2 B-D 3-D structural model required in nonlinear response history procedure Not explicit in BNBC-2020

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Horizontal Irregularity 5: Nonparallel System Irregularity

Refer to ASCE 7-10 Table 12.3-1

Horizontal Irregularity 5: Nonparallel System Irregularity

Nonparallel system Irregularity exists when the vertical lateral force-resisting elements are not parallel to or symmetric about the major orthogonal axes of the Seismic force-resisting system.

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Horizontal Irregularity 5: Nonparallel System Irregularity

Section SDC Description 12.5.3 C-F Orthogonal load combinations 2.5.13.1(b) Table D-F Permitted analytical procedure 12.6.1 ELF Permitted Also in BNBC-2020 12.7.3 B-D 3-D structural model required Not explicit in BNBC-2020 16.2.2 B-D 3-D structural model required in nonlinear response history procedure Not explicit in BNBC-2020

12.5, 2.5.13.1 Direction of Loading

12.5.2, 2.5.13.1(a) SDC B. The design seismic forces are permitted to be applied independently in each of two orthogonal directions and orthogonal interaction effects are permitted to be neglected.

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12.5, 2.5.13.1 Direction of Loading

12.5.3, 2.5.13.1(b) SDC C. Structures that have horizontal structural irregularity Type 5 of Table 12.3-1, shall use one of the following procedures.

12.5, 2.5.13.1 Direction of Loading

12.5.3, 2.5.13.1(b) SDC C. a. Orthogonal Combination Procedure. ELF, modal response spectrum, or linear response history analysis, with loading applied independently in any two orthogonal directions…

100% + 30%

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Horizontal Irregularity 5: Nonparallel System Irregularity

y 3

4 2

Horizontal Irregularity 5: Nonparallel System Irregularity

y y

Vx3 Vy3

Vx4 Vy4 Vx2 Vy2 EQx EQy x x

Vx1 Vy1 In-plane shear in shear walls from earthquakes in x and y directions

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Horizontal Irregularity 5: Nonparallel System Irregularity

y y V + 0.3V x3 y3 0.3Vx3 + Vy3

Vx4 + 0.3Vy4 V + 0.3V 0.3Vx4 + Vy4 x2 y2 0.3Vx2 + Vy2 EQx EQy x x

Vx1 + 0.3Vy1 0.3Vx1 + Vy1 Case 1 Case 2 Design in-plane shear in shear walls considering orthogonal effects is the maximum from Case 1 and Case 2

12.5, 2.5.13.1 Direction of Loading

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12.5, 2.5.13.1 Direction of Loading

12.5.3 , 2.5.13.1(c) SDC C. b. Simultaneous Application of Orthogonal Ground Motion.

Linear or nonlinear response history analysis, with orthogonal pairs of ground motion acceleration histories applied simultaneously.

Vertical Irregularities (Table 12.3-2)

1a. Stiffness – soft story 1b. Stiffness – extreme soft story (2000 IBC) 2. Weight (mass) 3. Vertical geometric 4. In-plane discontinuity in vertical lateral-force- resisting elements 5a. Discontinuity in lateral strength – weak story, 5b. Discontinuity in lateral strength – extreme weak story (ASCE 7-05/2006 IBC)

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Vertical Irregularities (Table 12.3-2)

Part 6, Chapter 1,Table 6.1.4 Vertical Structural Irregularities (Essentially Repeated in 2.5.5.3.2)

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2.5.17 Buildings with Soft Story Buildings with possible soft story action at ground level for providing open parking spaces belong to structures with major vertical irregularity [Figure 6.2.28(a)]. Special arrangement is needed to increase the lateral strength and stiffness of the soft/open storey. The following two approaches may be considered: (1) Dynamic analysis of such building may be carried out incorporating the strength and stiffness of infill walls and inelastic deformations in the members, particularly those in the soft storey, and the members designed accordingly.

2.5.17 Buildings with Soft Story

(2) Alternatively, when system overstrength factor, o, is not included in determining seismic load effects, the following design criteria are to be adopted after carrying out the earthquake analysis, neglecting the effect of infill walls in other stores. Structural elements (e.g columns and beams) of the soft storey are to be designed for 2.5 times the story shears and moments calculated under seismic loads neglecting effect of infill walls. Shear walls placed symmetrically in both directions of the building as far away from the centre of the building as feasible are to be designed exclusively for 1.5 times the lateral shear force calculated before.

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Vertical Irregularity 1a: Stiffness-Soft Story Irregularity

Refer to ASCE 7-10 Table 12.3-2

SOFT STORY STIFFNESS < 70% STORY STIFFNESS ABOVE OR < 80% [AVERAGE STORY STIFFNESS OF 3 STORIES ABOVE]

Vertical Irregularity 1a: Stiffness-Soft Story Irregularity

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Vertical Irregularity 1a: Stiffness-Soft Story Irregularity

Section SDC Description Table D-F Permitted analytical procedure 12.6.1 Neither ASCE 7 nor BNBC-2020 permits ELF

Vertical Irregularity 1b: Stiffness-Extreme Soft Story Irregularity

Refer to ASCE 7-10 Table 12.3-1

SOFT STORY STIFFNESS < 60% STORY STIFFNESS ABOVE OR < 70% [AVERAGE STORY STIFFNESS OF 3 STORIES ABOVE]

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Vertical Irregularity 1b: Stiffness-Extreme Soft Story

12.3.3.1:PROHIBITED IN SDC E & F!!

Areas where S1 0.75g Do not exist in Bangladesh

Vertical Irregularity 1b: Stiffness-Extreme Soft Story

Section SDC Description Table D-F Permitted analytical procedure 12.6.1 Neither ASCE 7 nor BNBC-2020 permits ELF

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Vertical Irregularity 2: Weight (Mass) Irregularity

Refer to ASCE 7-10 Table 12.3-2

STORY MASS > 150% ADJACENT STORY MASS (A ROOF THAT IS LIGHTER THAN THE FLOOR BELOW NEED NOT BE CONSIDERED)

Vertical Irregularity 2: Weight (Mass) Irregularity

Section SDC Description Table D-F Permitted analytical procedure 12.6.1 Neither ASCE 7 nor BNBC-2020 permits ELF

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Vertical Irregularities Exception 1 to 12.3.2.2 Vertical structural irregularities of Types 1a, 1b, or 2 in Table 12.3-2 do not apply where no story drift ratio under design lateral seismic force is greater than 130 percent of the story drift ratio of the next story above. Torsional effects need not be considered in the calculation of story drifts. The story drift ratio relationship for the top two stories of the structure are not required to be evaluated.

Vertical Irregularities Exception 2 to 12.3.2.2 Irregularities Types 1a, 1b, and 2 of Table 12.3-2 are not required to be considered for one-story buildings in any seismic design category or for two-story buildings assigned to Seismic Design Categories B, C, or D.

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Typical Plan of Example Building

1 2 3 4 5 6 7 8

26 c- 0 s 26 c- 0 s 26 c- 0 s 26 c- 0 s 26 c- 0 s 26 c- 0 s 26 c- 0 s

22ccc

B N

22ccc

Typical Elevation of Example Building

7 11@ 12c-0cc =132c-0cc 6

16c-0cc

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Vertical Structural Irregularity

2nd story Stiffness ratio = 12 ft Stiffness of first to second story = 3 3 1st story (1/16 )/(1/12 ) =0.42 < 0.60 16 ft

Thus, per Table 12.3-2, Stiffness-Extreme Soft Story Irregularity (Vertical Irregularity Type 1b) should be considered.

Vertical Structural Irregularity

Exception 1 to ASCE 7-05 Section 12.3.2.2 Vertical structural irregularities of Type 1a, 1b, or 2 in ASCE Table 12.3-2 do not apply where no story drift ratio under design lateral seismic force is greater than 130 percent of the story drift ratio of the next story above.

§ G 1e · GG 1e2e ¨ ¸ 3.1 © h1 ¹ h2

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Analysis Results (E-W Direction) Lateral forces, displacements and interstory drifts due to seismic forces in E-W directions

Force Story d (in.) d (in.) D (in.) (kips) xe x 12 275 3.51 19.31 0.45 11 268 3.43 18.86 0.75 10 234 3.29 18.11 1.05 9 202 3.10 17.06 1.31 8 171 2.86 15.75 1.53 7 142 2.59 14.22 1.72 6 114 2.27 12.50 1.86 5 89 1.93 10.64 1.98 4 65 1.58 8.66 2.05 3 44 1.20 6.61 2.12 2 26 0.82 4.49 2.12 1 12 0.43 2.37 2.37

Vertical Structural Irregularity

E-W Direction:

§ G 1e · § .0 43 · ¨ ¸ ¨ ¸ .0 00224 © h1 ¹ © u1216 ¹ GG .0 82 .0 43 3.1 1e2e 3.1 .0 00352 ! .0 00224 h2 u1212 Thus, structural irregularity of Type 1b is deemed NOT to exist.

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Vertical Irregularity 2: Weight (Mass) Irregularity

Irregularity exists if the effective mass of any story is more than 150% of the effective mass of an adjacent story. Exception: Irregularity does not exist if no story drift ratio is greater than 1.3 times drift ratio of story above.

Exception: Not required to be considered for one-story buildings in any seismic design category or for two-story buildings assigned to Seismic Design Categories B, C, or D.

Exceptions apply to Types 1 a and b as Source: FEMA well as to Type 2.

Vertical Irregularity 3: Vertical Geometric Irregularity

Refer to ASCE 7-05 Table 12.3-2

HORIZONTAL DIMENSION OF LATERAL FORCE-RESISTING SYSTEM IN STORY > 130% OF THAT IN ADJACENT STORY

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Vertical Irregularity 3: Vertical Geometric Irregularity

di+1 Irregularity exists if the dimension of the lateral force resisting system at di any story is more than 130% of that for any adjacent story

di-1

Source: FEMA

Figure 6.2.28 Different types of vertical irregularities of buildings

(c) Vertical geometric irregularity (setback structures) This irregularity exists for buildings with setbacks with dimensions given in Figure 6.2.28(c).

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Vertical Irregularity 3: Vertical Geometric Irregularity

Section SDC Description Table D-F Permitted analytical procedure 12.6.1 Neither ASCE 7 nor BNBC-2020 permits ELF

Vertical Irregularity 4: In-Plane Discontinuity

Refer to ASCE 7-10 Table 12.3-2

An in-plane offset of the lateral force resisting elements greater than the length of those elements Figure 6.2.28(d)

THERE IS AN IN-PLANE OFFSET OF A VERTICAL SEISMIC FORCE-RESISTING ELEMENT RESULTING IN OVERTURNING DEMANDS ON A SUPPORTING BEAM, COLUMN, TRUSS, OR SLAB.

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Vertical Irregularity 4: In-Plane Discontinuity - BNBC-2020

Vertical Irregularity 4: In-Plane Discontinuity

Irregularity exists if there is an in- plane offset of a vertical seismic force-resisting element resulting in d overturning demands on a supporting beam, column, truss, or offset slab.

Source: FEMA

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Vertical Irregularity 4: In-Plane Discontinuity

Vertical Irregularity 5a: Weak Story Irregularity

Refer to ASCE 7-10 Table 12.3-2

“WEAK STORY” LATERAL STRENGTH < 80% LATERAL STRENGTH ABOVE STORY LATERAL STRENGTH = TOTAL STRENGTH OF SEISMIC FORCE-RESISTING ELEMENTS

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Vertical Irregularity 5a: Weak Story Irregularity

12.3.3.1:PROHIBITED IN SDC E & F!!

Areas where S1 0.75g Do not exist in Bangladesh

Vertical Irregularity 5a: Weak Story Irregularity

Section SDC Description Table D-F Permitted analytical procedure 12.6.1 ELF permitted in ASCE 7-05, not in BNBC-2020

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Vertical Irregularity 5b (worst of the worst): Extreme Weak Story Irregularity

Refer to ASCE 7-10 Table 12.3-2

“WEAK STORY” LATERAL STRENGTH < 65% LATERAL STRENGTH ABOVE STORY

LATERAL STRENGTH = TOTAL STRENGTH OF SEISMIC FORCE- RESISTING ELEMENTS

Vertical Irregularity 5b (worst of the worst): Extreme Weak Story Irregularity

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Vertical Irregularity 5b (worst of the worst): Extreme Weak Story Irregularity

12.3.3.1:PROHIBITED IN SDC D, E & F!!

SDC E,F: Areas where S1 0.75g Do not exist in Bangladesh

Vertical Irregularity 5b (worst of the worst): Extreme Weak Story Irregularity 12.3.3.2 Extreme Weak Stories. Structures with a vertical irregularity Type 5b as defined in Table 12.3-2, shall not be over two stories or 30 ft (9.1 m) in structural height, hn. EXCEPTION: The limit does not apply where the “weak” story is capable of resisting a total seismic force equal to :o times the design force prescribed in Section 12.8. Have not found similar requirement in BNBC-2020.

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Vertical Irregularity 5a, 5b: Weak Story and Extreme Weak Story Irregularities

Irregularity (5a) exists if the lateral strength of any story is less than 80% of the strength of the story above.

An extreme irregularity (5b) exists If the lateral strength of any story is less than 65% of the strength of the story above.

Irregularities 5a and 5b are NOT PERMITTED in SDC E or F. Irregularity 5b not permitted in SDC D.

Source: FEMA

PART 7 NONSTRUCTURAL COMPONENTS AND NONBUILDING STRUCTURES

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Main Topics

Code Requirements for Nonstructural Components Code Requirements for Nonbuilding Structures 2.5.18 Nonstructural Component vs Nonbuilding Structure

2006 IBC Section 1613.1 References ACSE 7-05 for Seismic

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Applicable ASCE 7-05 Chapters

Chapter 13: Nonstructural Components Chapter 15: Nonbuilding Structures

ASCE 7-05 Chapter 13 Nonstructural Components Architectural (Section 13.5) Mechanical & Electrical (Section 13.6)

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Architectural Components (Table 13.5-1) (Table 6.2.22) • Nonstructural walls & partitions • Parapets & chimneys • Exterior nonstructural wall elements & connections • Veneer • Penthouses • Ceilings •Cabinets • Access floors •Signs • Billboards • Appendages •Glazing

Mechanical Components (Table 13.6-1) (Table 6.2.23)

Boilers and furnaces HVAC Piping systems Engines Turbines Fans Furnaces Chillers Elevators Escalators

OSHPD/FDD

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Electrical Components (Table 13.6-1) (Table 6.2.23)

Conduit Bus ducts Cable trays Lighting

When Do Provisions Apply? (Exceptions: Section 13.1.4 (2.5.15))

SDC B • Arch: Parapets • Arch: when > 1 ( > 1) SDC C •Arch: All • Elec & Mech: when > 1 ( > 1) SDC D, E, & F • Arch, Elec, & Mech: basically always

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What is ( )?

( ) is Component Importance Factor ( ) is set forth in Section 13.1.3 (2.5.15.1) ( ) is either 1.0 or 1.5

What Force Do You Need to Design For? (ASCE 7-05 Section 13.3.1)

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What Force Do You Need to Design For? (BNBC-2020 Section 2.5.15.3)

What is ?

is expected horizontal peak ground acceleration (in g) for design

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What is ( )?

( ) is Amplification Factor ( ) is set forth in Tables 13.5-1 (Table 6.2.22) for arch & 13.6-1 (Table 6.2.23) for mech and elec ( ) is either 1.0 or 2.5, with one exception

What Force Do You Need to Design For? (Section 13.3.1) (2.5.15.3)

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Explanation of Equation

1.2SDS

AB = 0.4SDS (1+2zB/h) B

Floor Acceleration h Distribution zB A AA= 0.4SDS (1+2zA/h)

z 0.4SDS A

What Force Do You Need to Design For? (Section 13.3.1) (2.5.15.3)

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What is ?

is Component Response Modification Factor is set forth in Tables 13.5-1 & 13.6-1 (Tables 6.2.22 & 6.2.23) ranges from 1.0 to 12.0

Seismic Relative Displacements

The effects of seismic relative displacements are required to be considered (Section 13.3.2) (2.5.15.4).

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Special Certification

Q: Where in the code? A: ASCE 7-05 Section 13.2.2 & 2006 IBC Section 1708.5. Not there in BNBC. Q: Applies to what? A: SDC C-F mech & elec equipment with > 1* and SDC C-F components with hazardous contents with > 1* Q: Requires what? A: Special Certification

*Designated seismic system is defined in ASCE 7-05 Section 11.2 (Ip>1.0)

Special Certification

For Mechanical and Electrical Equipment……show that equipment remains operable following design earthquake by: Shake table testing in accordance with Section 13.2.5 or Experience data in accordance with Section 13.2.6 or Analysis

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Special Certification

For Components with Hazardous Contents…show that containment is maintained following design earthquake by: Shake table testing in accordance with Section 13.2.5 or Experience data in accordance with Section 13.2.6 or Analysis

2009 IBC Chapter 17 Periodic Special Inspection Requirements 1707.6 Storage racks & access floors 1707.7 Architectural components 1707.8 Mechanical & electrical components

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Anchorage of Nonstructural Components Design Forces Section 13.4.1 Anchors in Concrete Section 13.4.2 Installation Conditions Section 13.4.3 Multiple Attachments Section 13.4.4 Power Activated Fasteners Section 13.4.5 Friction Clips Section 13.4.6

Specifics for Arch Components

Exterior Walls & Connections Section 13.5.3 Glass Sections 13.5.4 & 13.5.9 Suspended Ceilings Section 13.5.6 Access floors Section 13.5.7.2 Partitions Section 13.5.8

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Specifics for Mech & Elec Components

Utility & Service Lines Section 13.6.6 HVAC Ductwork Section 13.6.7 Piping Systems Section 13.6.8 Boilers & Pressure Vessels Section 13.6.9 Elevators & Escalators Section 13.6.10

Nonbuilding Structures What Are They?

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Requirements for Nonbuilding Structures in BNBC-2020 BNBC-2020 Section 2.5.18 points to Chapter 15 of ASCE 7-05 for nonbuilding structures. “Calculation of seismic design forces on non-building structures (e.g. chimney, self-supported overhead water/fluid tank, silo, trussed tower, storage tank, cooling tower, monument and other structures not covered in Sec 2.5) shall be in accordance with "Chapter 15: Seismic Design Requirements for Non- Building Structures, Minimum Design Loads for Buildings and Other Structures, ASCE Standard ASCE/SEI 7-05" complying with the requirements of Sec 2.5 of this Code.”

Exceptions: Section 11.1.2, 4.

Vehicular bridges Electrical transmission towers Hydraulic structures Buried utility lines Nuclear reactors

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Nonbuilding Structures Similar to Buildings

Nonbuilding Structures NOT Similar to Buildings

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Similar to Buildings: What Force Do You Need to Design For?

See Section 15.4.1. Same as for buildings. Use Table 12.2.-1 , plus Table 15.4-1. Calculate period per Section 15.4.4.

Table 15.4- 1 Seismic Coefficients for Nonbuilding Structures Similar to Buildings

Structural System and Nonbuilding Structure Detailing Height Limits (ft)a R ȍ0 Cd Type Requirements A &B C D E F

Building frame systems:

Ordinary steel concentrically braced AISC 341 3.25 2 3.25 NL NL 35b 35b NPb frame

With permitted height AISC 341 2.5 2 2.5 NL NL 160 160 100 increase

With unlimited height AISC 360 1.5 1 1.5 NL NL NL NL NL

178

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NOT Similar to Buildings: What Force Do You Need to Design For? See Section 15.4.1. Same as for buildings but with different , , table (Table 15.4-2) & more “minimum checks” on base shear. Calculate period per Section 15.4.4.

Design Force Equations

SWCV S S C D1 d DS dTTfor S (R/I)T (R/I) L TS D1 L !TTfor T2 (R/I) L t 0.03 0.8S t 1 t0.6gSwhere (R/I) 1

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What is ?

is the Importance Factor is set forth in Section 15.4.1.1, which references Table 11.5-1 is either 1.0, 1.25, or 1.5

How Do You Determine T?

See Section 15.4.4 Fundamental Period ……Equations 12.8-7, 12.8-8, 12.8-9, and 12.8-10 shall not be used for determining the period of a nonbuilding structure.

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Specifics for Similar to Buildings

Pipe Racks Section 15.5.2 Steel Storage Racks Section 15.5.3 Electrical Power Generating Facilities Section 15.5.4

Towers Supporting Tanks & Vessels Section 15.5.5

Piers & Wharves Section 15.5.6 (accessible to the public)

Specifics for NOT Similar to Buildings

Earth-Retaining Structures Section 15.6.1 Stacks & Chimneys Section 15.6.2 Amusement Structures Section 15.6.3 Special Hydraulic Structures Section 15.6.4 Secondary Containment Structures Section 15.6.5 Tanks & Vessels Section 15.6.7

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What Is It?

Nonstructural Component or Nonbuilding Structure

What Is It?

Nonstructural Components Ch. 13 Access floors Air conditioning units Escalator Components Air distribution boxes Evaporators Nonbuilding Air handlers Furnaces Air separators Generators Structures Not Battery racks Heat exchangers Similar to Boilers HVAC Buildings Cabinet heaters Inverters Cabinets Lighting fixtures Ch. 15 Cable trays Manufacturing equipment Billboards and Signs Ceilings Motor control centers Bins Amusement structures Chillers Motors Chimneys Hoppers (elevated) Communication equipment Panel boards Conveyors Monuments Compressors Parapets Stacks Silos (cast-in-place concrete having Computers Penthouse (except where framed by an Tanks walls to foundation) Ductwork extension of the building frame) Towers Storage racks (steel) Electrical conduit Piping Vessels Elevator Plumbing Cooling Towers Engines Process equipment Switch gear Pumps Transformers Wall panel Tubing Walls Turbines Water heaters Veneer Vibration isolated components and systems

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These Can Be Either

Billboards and Signs Tanks Bins Towers Chimneys Vessels Conveyors Cooling Towers Stacks

What Are Some Differences? ~ WARNING ~ What you are about to see….

For Guidance Only Generalizations Made Generalizations Don’t Always Apply Common Sense Necessary

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What Are Some Differences? SIZE Nonstructural Components Nonbuilding Structures

Small enough to fit in Typically large building Somewhere around 10’ (arbitrary!) tall Usually transported in one piece on a truck

Designer’s Option

Designer always has the option of calculating both ways and using more conservative answer.

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What Are Some Differences?

ASSEMBLY LOCATION

Nonstructural Components Nonbuilding Structures

Usually requires no Usually assembled at jobsite assembly at jobsite Weight is likely small relative to structure’s weight

What Are Some Differences?

BASIS FOR CONSTRUCTION

Nonstructural Components Nonbuilding Structures

Usually function is for arch, Usually to maintain mech, elec purposes structural integrity Usually constructed to resist gravity and lateral loads

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Example: Seismic Design of Parapets

Weight of the parapet per linear foot is = 24.52 x 0.9 x 0.18 = 3.97 kN/m

The seismic lateral force acting at the centroid of the parapet is given by ASCE Equation (13.3-1) as = Where = component importance factor = 1.0

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Example: Seismic Design of Parapets

SDS = 0.5g

Wp = weight of parapet = 3.97 kN/m ap = component amplification factor from ASCE Table 13.5-1 = 2.5 h = height of roof above the base = 6 m. z = height of parapet at point of attachment = 6 m.

Example: Seismic Design of Parapets

= component response modification factor from ASCE Table 13.5-1 = 2.5

= (0.4 x 2.5 x 0.5 × 1.0 / 2.5) (1 + 2 x 6/6) = 0.6 = 2.38 kN/m

Neither ASCE Equation (13.3-2) nor (13.3-3) governs, and the bending moment at the base of the parapet is

= 0.45 = 1.07 kN-m/m

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Questions? Thank you