Standard Precast Sections Show Versatility and Economy in Israel's New Pedestrian Bridges This article describes the aesthetic considerations, design criteria and structural features of three new precast, prestressed concrete pedestrian bridges crossing the recently expanded highway that runs between Tel Aviv and Haifa in Israel. The use of standard precast components allowed the designer of the bridges to accommodate the unique conditions of each bridge site in an economical manner without ca using any disruption to vehicular traffic flow during construction. Eliezer Shamir, P.E. Partner Shamir Posn er Brown Consulting Engineers Ltd . he main highway connecting the ing site conditions and geometries. Te l Aviv, Israel cities of Tel Aviv and Haifa in The result is a "family" of bridges of T Israel is very congested along its the same aesthetic concept that use entire length. Recently, it was widened similar structural components while to four lanes in each direction, all each maintains its own "personality" Long-time PCI Profess ional Member junctions were upgraded to the inter­ within the group. A strong impression Eliezer Sh amir has been a consulting change type, and three pedestrian of continuity, elegance, stability and engi neer in Israel for the last 30 years, spec ial izing in the design of prestressed crossings were erected, mainly in rural simplicity is achieved due to a well­ concrete structures and bridges. sections of the highway. balanced composition of basic struc­ Currently, he is a member of the Israel A standard pedestrian bridge was tural components. Association of Engineers and Architects developed to fulfill the needs of small The most dominant feature of the Structural Division and Prestressed villages and to blend in with the exist­ bridge is the corner towers (see Figs. 4 Concrete Group. ing environments. All three bridges and 5). The standard design calls for were based on this design and have the either a four-leg corner tower or a same general appearance: two main three-leg corner tower that allows for spans up to 29 m (95 ft) long and two a straight-line bridge, a 90-degree side ramps. turn, or 120-degree tum in alignment, Figs. 1, 2 and 3 show three types of while maintaining the same general bridges with a single ramp, two side appearance on the whole. Until now, ramps and a folded ramp. The four­ only four-leg towers had been in use. leg towers can vary. An effort was made to emphasize Despite the rigid basic shapes of the the contrast between the towers and the bridge components, various configu­ deck because this is the major factor rations were implemented to fit differ- contributing to the general impression 116 PCI JOURNAL of smoothness and continuity of the deck. This was achieved mainly through: • A deck that passes through vertical components of piers and towers, rather than just resting upon them. • Simplicity achieved through straight lines for all structural components. • Placement of the deck behind pier vertical components, and totally de­ Fig. 1. Udim Bridge. One side four-leg corner tower bridge. tached from them. • Deck girders that compose a contin­ uous line starting at the lower edge of one ramp and ending at the lower point of the opposite ramp, empha­ sized by the paint-coated steel railing. • Slope changes only at corner towers. • Pier vertical components that rise above deck top levels. • A concrete face for the columns that is smooth fair faced, while the con­ crete face of deck girders is textured Fig. 2. Yakum Bridge. Two side ramps, double four-leg corner tower bridge. fair faced. STRUCTURAL SYSTEM Due to the use of precast concrete components, all of the bridges were constructed without causing any in­ terruption to highway traffic flow. The main structural elements of the bridges are: Foundations - Bored piles of Fig. 3. Rishpon Bridge. Double four-leg corner tower bridge, one stra ight ramp, one cast-in-place concrete with socket­ folded ramp. type pile caps. Corner Towers - Four precast re­ inforced concrete columns per tower, Fig. 4. connected with cast-in-place trans­ Rishpon Bridge. verse beams to form the four-leg Bridge ramp corner tower, or three-leg tower (see Figs. 6 on a four-leg tower. and 7). As an alternative, precast rein­ forced concrete beams can be used for the connection, employing an "invisi­ ble corbel" connection such as the BSF beam-to-column connection man­ ufactured by JVI Accessories, Inc. Intermediate Piers - Two precast concrete reinforced columns per pier, connected with a cast-in-place trans­ verse beam to form the double-leg pier. The same alternative precast beam as for the corner tower, can be used. Vertical columns are placed into socket-type pile caps and grouted. Deck Girders - Two C-shaped precast, prestressed concrete girders per span, facing each other. A typical November-December 1996 117 cross section of a deck girder is shown in Fig. 8. The maximum span is 29.50 m (97 ft). All girders are pretensioned with 12.7 mm (lh in .) diameter 270k straight strands (some of the strands are debonded towards the girder ends). The external face of the girder is tex­ tured (vertical "corduroy" type, with chipped slots). All exposed surfaces are fair faced concrete. Slots are al­ ways vertical, even for inclined girders of ramps. Deck Plate - Precast reinforced concrete deck panels placed side-by­ side on the lower flange of the deck girders, and connected with a cast-in­ place concrete topping that provide structural integrity. An overall cover Fig. 5. Folded ramp at Rishpon Bridge . of architectural anti-slide Granolite layer (colored round, edges exposed aggregate concrete mjx) is applied for the final walking surface. The same structural system is used for the bridge span and the sloped ramps. The average ramp slope is ap­ proximately 14 percent, obtained by the combination of a 10 percent slope walking surface and 70 mm (2.75 in.) drops in elevation every 1750 mm (69 in .). CAST IN PLACE PARAPET Bearings - Reinforced neoprene <SIMILAR CROSS SECTION AND r!NISH AS LONG. bearings only at end supports (lower GIRDERS> CONI'£CTS GIRDERS side of ramp girders near ground TO TOWER FRAME surface). Connections - Generally speak­ ing, all connections are rigid and monolithic to provide full structural integrity, except for the free supports for ramp girders at their lower side, Fi g. 6. Four-leg corner tower. which use R.N. bearings. Connections between pile caps and columns are the grouted socket-type and are considered as fixed connections with full moment and shear resistance. Connections between deck panels and girders are achieved using special threaded inserts, embedded in the pre­ cast longitudinal girders. These con­ nections are welded (or/and over­ lapped) with reinforcement dowels embedded in precast deck panels, to­ gether with a cast-in-place concrete topping. This connection is considered as a full moment and shear resistance connection. A typical girder-to-deck connection is shown in Fig. 9. Connections between longitudinal deck girders and tower (or pier) Fig. 7. Three-leg corner tower. columns are achieved using special 118 PCI JOURNAL • Temperature changes per Israeli 220 RAILING Standard 1227 A structural analysis was performed EXPOSED SURF ACE PRECAST PRESTRESSED using STRAP three-dimensional soft­ FAIR FACED CONCRETE CONCRETE, VERTICAL LONGITUDINAL GIRDER SLOTS TEXTURED ware, and PRETTEN software for pre­ stressing analysis and design. The inter­ face between the piles and the ground is modeled using elastic springs and elastic foundations methodology. Special measures were taken to con­ trol the twist of the C-shaped longitu­ Fig. 8. Typical section of deck girder. dinal girders with respect to their shear (flexural) center due to the girder self weight and prestressing, mainly by compensating pretensioning eccentric­ ity. As a result, the maximum lateral deflection was approximately 25 mm (1 in.) for the 29 m (95 ft) long girder. Secondary moments, arising out of changes in the structural scheme from a simply supported beam to an inde­ p PRESTRESSED terminate space frame during con­ LONG. GIRDER struction, were taken into account. This required additional prestressing for positive bending moments at midspans, and special bottom rein­ forcement at the supports. SCHEDULE AND COSTS The construction time for all three 55 bridges, including general site devel­ opment, was 5 months. Erection time Fig. 9. Girder-to-deck connection. for the superstructure on site was one month per bridge. The total cost of all three bridges threaded inserts embedded in girders DESIGN CRITERIA was approximately $500,000. and columns overlapping (or welded AND STRUCTURAL to) each other, together with cast-in­ ANALYSIS place concrete. CREDITS This connection is always hidden The structure as a whole was mod­ Owner: Israel Ministry of Housing­ behind the columns so it cannot be eled as a space frame (three-dimen­ Public Works Department, Tel seen by drivers of vehicles and/or sional) and is designed to withstand Aviv, Israel pedestrians. It provides full integrity the following loads: Design Engineers: Shamir Posner for the deck, piers and towers, in • Self weights Brown Consulting Engineers Ltd., order to obtain a three-dimensional • Live loads per Israeli Standard 1227 Tel Aviv, Israel space-frame structural scheme. The • Wind loads per Israeli Standard 412 Contractor: Maagan Ltd., in coopera­ connection is considered to be partly • Accidental vehicle impact loads per tion with Cemenkal Ltd., Tel Aviv, hinged, providing full shear resistance Israeli Standard 1227 Israel between girders and between girders • Earthquake loads per AASHTO Precast Prestressed Concrete Manu­ and columns, and only limited mo­ Specifications and Israeli Standard facturer: Solei Boneh Ltd., Precast ment resistance. 413 Division, Tel Aviv, Israel November-December 1996 119 .