docStructural Design and Construction Practice of Precast Concrete
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Structural Design and Construction Practice of Precast Concrete
Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete 00 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete International Seminar on Design and Construction of Precast Structures in Seismic Regions October 2015, Chile Structural Design and Construction Practice of Precast Concrete Buildings in Japan Fumio Watanabe Emeritus Professor of Kyoto University Executive Technical Advisor of Takenaka Corporation [email protected] Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete I would like to express my hearty thanks to Prof. Patricio Bonelli (University Frederico Santa Maria, Valparaiso) and Dr. August Holmberg (President of Chilean Cement and Concrete Institute), who kindly invited us to nice country Chile in the southern hemisphere. I would express my hearty sympathy to the Chilean people who suffered the heavy losses during the great earthquake on September 16. CHILE 01 JAPAN Seismic Countries Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 1. Outline of Japanese Seismic Design Method 2. Requirements for Structural Equivalency to Monolithic Construction 3. Design Equations fro Interface Shear 4. Typical Detailing of Precast Connection Part 2 5. Design Example of Precast Connection 6. Example of Precast Reinforced Concrete Building 7. Example of Precast Prestressed Concrete Building 8. Example of Precast Prestressed Concrete Stadium 9. Structural Damage in Past Earthquake 02 Dr. Tsutomu Komuro at Taisei Corporation Prof. Makoto Maruta at Shimane University (Kajima Corporation) Prof. Minehiro Nishiyama at Kyoto University Dr. Masaru Teraoka at Kure National Collage of Technology (Fujita) Dr. Hideki Kimura at Takenaka Corporation Mr. Hisato Okude at Takenaka Corporation Dr. Yuuji Ishikawa at Takenaka Corporation Dr. Hassane Ousalem at Takenaka Corporation Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 1. Outline of Japanese Seismic Design Method Hukui Earthquake (1948, M7.1) Establishment of modern seismic design code (Building Standard Law) (1951) Tokachi-Oki Earthquake (1968, M7.9) Intensification of the requirement to lateral reinforcement (1971) Miyagiken-Oki Earthquake (1978, M7.4) Drastic revision of Building Standard Law (1981: currently used) Hyogo-Ken Nanbu (Kobe) Earthquake (1995, M7.2) 03 Partial revision of 1981 Building Standard Law (1995) Adoption of performance based design process (2000) Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 1. Outline of Japanese Seismic Design Method Design for Gravity Load Allowable stress design Flexural Design ' Allowable stress of concrete = fc / 3 Allowable stress of re-bar ≤ 215 N / mm2 for deformed bar A: Conventional Seismic Design Method (most widely used in Japan and completely revised in 1981) 04 Conditions: Buildings less than 60 meters and without isolation systems, damping devices and other response control devices Allowable stress design for minor earthquake Flexural Design Allowable stress of concrete = 2 fc' / 3 Allowable stress of re-bar ≤ specified yield strength Capacity design for major earthquake Lateral story shear strength should be greater than the code specified story shear strength which depends on the structural ductility. Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 1. Outline of Japanese Seismic Design Method A: Conventional Seismic Design Method Capacity design for major earthquake Required lateral strength at each story is determined based on the elastic response for design base shear coefficient of unit and the lateral story shear distribution function. Required lateral strength at each story can be reduced depending on the structural ductility. This reduction factor ranges from 0.30 (for special ductile moment frames) to 0.55 (for elastic responding structures). Qun = Ds FesQud Qun Qud Fes Ds 05 (Eq. 1) Ds = 0.55 =required story shear strength =elastic story shear response =coefficient for structural irregularity 1.0 ≤ Fes =reduction factor based on the structural ductility 0.3 ≤ Ds ≤ 0.55 Ds = 0.30 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 1. Outline of Japanese Seismic Design Method A: Conventional Seismic Design Method Capacity design for major earthquake Qud = Wi ZRt AiCo (Eq. 2) Co =standard base shear coefficient and 1.0 for major earthquake Z =zoning coefficient and ranged from 0.7 to 1.0 Wi =weight of building above i-th story 06 Roof level 0 0. 2 0. 4 αi T=4.0 sec. T=0 Soft soil 0.8 T=0.5 sec. T=0.1 sec. 0. 6 0.6 R t 0.4 Medium soil 0.2 0.8 1. 0 1 Ground level 0 1 2 3 4 5 6 Lateral story shear distribution factor Ai 0 0 Hard soil 0.5 1 1.5 2 2.5 Natural period of a building T in sec. Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 1. Outline of Japanese Seismic Design Method B: Advanced Verification Procedure (Revised in 1981) All types of buildings can be designed by this procedure Dynamic time history analysis against earthquake ground motion is required to assure the design criteria for structural responses such as maximum interstory drift, story ductility, member ductility and others. As input ground motions, past strong ground motion records and artificial waves are used, where artificial waves should meet the code specified standard design spectrum at the engineering bedrock. Phase, duration time and site condition (surface geology) are also considered. The engineering bedrock is defined as a thick soil stratum that shear wave velocity is not less than 400 meter/ sec. Standard Design Spectrum at Engineering Bed Rock 07 Part 1 - 1. Outline of Japanese Seismic Design Method C: Performance based design method (Newly established in 2000) Required lateral strength and structural ductility are given at an intersection point (performance point) of the demand spectrum at building base and the capacity spectrum for superstructure. sec 0.5 h=0.05 T= The keys of design are the proper evaluation of equivalent damping factor of a superstructure and the reliable estimation of input ground motion at building base. Because the standard design spectrum (response spectrum) is given at the engineering bedrock Demand spectra for different Demand Spectra fordamping Different valuesDamping calculated Values Calculated Spectral Acceleration Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete h=0.1 0.4g T= 0 1. se c S /S h 0 .0 5 =1.5/(1+10h) h=0.3 Performance point T=2 .0 s e c 0.2g 1/200 Spectral Displacement Determination of Performance Point 08 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 2. Requirements for Structural Equivalency to Monolithic Construction In Japan, precast concrete building structures are being constructed that attempt to emulate seismic performances of cast-in-place monolithic structures. The reason is that Japanese Building Standard Law and Enforcement Order for structural design have been established based on the structural behavior of monolithic reinforced and prestressed concrete structures. Equivalent monolithic structural behaviour is generally demonstrated by tests on precast beam-column subassemblages and other structural sub-assemblies. Experimentally observed data is compared with that of simultaneously constructed pair specimen or with past experimental data in view of lateral stiffness, lateral strength, structural ductility and hysteretic behaviour (energy dissipation). 09 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 2. Requirements for Structural Equivalency to Monolithic Construction Beam column arrangement Beam bar welding 10 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 2. Requirements for Structural Equivalency to Monolithic Construction (1) Lateral strength at yielding should be greater or equal to that of emulated monolithic construction (2) Drift at yielding should be greater than 0.8Ry and not greater than 1.2Ry of emulated monolithic construction (3) These condition should be satisfied up to 2 % drift AIJ proposal for structural equivalency (a) Envelop curve 11 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 2. Requirements for Structural Equivalency to Monolithic Construction (b) Degradation and (c) Energy dissipation With regard to the degradation of load carrying capacity during seismic load cycling, the maximum load in the second cycle should be greater than 80% of that in the first cycle in the same drift amplitude. Energy dissipation of a precast system in second loading cycle should not be smaller than 80% of that of emulated monolithic construction 12 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 2. Requirements for Structural Equivalency to Monolithic Construction Monolithic pair specimen Precast specimen Japanese tests on equivalent monolithic precast beam-column assemblage (Courtesy of Dr. Masaru Teraoka at Fujita Cooperation) 13 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 2. Requirements for Structural Equivalency to Monolithic Construction Precast Wall Specimen tested by Hassane Ousalem at Takenaka Corporation 14 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 2. Requirements for Structural Equivalency to Monolithic Construction Testing Setup and Obtained Load Displacement Curve Hassane Ousalem et al ;Journal of Structural Engineering, Vol.61B, March 2015 15 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 2. Requirements for Structural Equivalency to Monolithic Construction Testing Setup and Obtained Load Displacement Curve Hassane Ousalem et al ;Journal of Structural Engineering, Vol.61B, March 2015 15-1 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 2. Requirements for Structural Equivalency to Monolithic Construction Example of Rebar Splice for Seismic Connection Grout injection Re-bar Mortar Grout Type Non-shrink grout 無収縮グラウト Sleeve Threaded Screw Type Epoxy injection Grout outlet Seal material Specifications approved by the Authority 1. Weather condition 2. Temperature range 3. Correct materials 4. Usable time after mixing of grout or epoxy materials 5. Correct insert length of rebar into sleeve 6. Perfect injection of grout or epoxy 7. Fixing re-bar and sleeve until hardening of grout or epoxy 16 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 2. Requirements for Structural Equivalency to Monolithic Construction Requirements for Rebar Splice for Seismic Connection (Rank A) 4 cycles 20 cycles Elastic 2ε y Slip<0.3mm 4 cycles 5ε y Re-bar Coupler Grout injection Slip<0.9mm Grout Re-bar Final fracture should occur at the base material One Example 17 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 3. Design Equations fro Interface Shear AIJ proposal : Basic design equations for joint (1) Friction (shear strength) Normal stress τ u = µσ n (Vu = µ N ) (3) Friction Coefficient (ACI310-02) 18 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 3. Design Equations fro Interface Shear AIJ proposal : Basic design equations for joint (1) Friction (shear strength) Friction resistance due to flexural compression a Vu = µC = µ ( M / j ) = µ V > V j (4) a µ> j Design condition 19 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 3. Design Equations fro Interface Shear AIJ proposal : Basic design equations for joint (2) Shear Friction (shear strength) τ u = µ ( ρ sσ y + σ o ) ρs σy σo Reinforcement ratio ' (5) τ u < 0.3 fc ' f c Compressive strength of concrete Yield strength of reinforcement (less than 800MPa) Normal stress µ Friction coefficient (ACI318-02) To suppress the slip deformation at maximum strength less than 0.5 mm, the shear strength should be taken as a half of calculated one (excepting for ultimate limit state design). 20 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 3. Design Equations fro Interface Shear AIJ proposal : Basic design equations for joint (3) Qdowel Dowel Action (shear strength) 2 Qdowel = 1.3db ' fcσ y Qdowel (6) Qdowel = 1.3db2 fc'σ y (1 − α 2 ) (7) α = σ s /σ y db fc' α : Bar diameter (mm) : Concrete strength (MPa) σ y : Yield strength of re-bar (MPa) σ s : Tension stress of re-bar (MPa) : Stress ratio of re-bar 21 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 3. Design Equations fro Interface Shear AIJ proposal : Basic design equations for joint (4-1) Shear Key (shear strength) Concrete bearing Vl1 = β ' f cl n ∑ wi xi (8-1) i =1 n Vr1 = β xi wi xi ' f cr ∑ wi xi i =1 (8-2) Width of a key Height of a key β Bearing strength factor: 1 Vbearing = Smaller of ( Vr1 or Vl1) 22 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 3. Design Equations fro Interface Shear AIJ proposal : Basic design equations for joint (4-2) Shear Key (shear strength) Concrete shear Vl 2 = 0.5 Vr 2 = 0.5 xi wi ai bi 0.5 ' f cl ' f cr n ∑ wi ai (9-1) ∑ wibi (9-2) i =1 n i =1 Width of a key Bottom length of a key Tens. strength ' f cl of concrete Vshear = Smaller of ( Vr 2 or Vl 2 ) 23 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 3. Design Equations fro Interface Shear AIJ proposal : Basic design equations for joint (4) Shear Key (shear strength) Shear strength of a set of shear keys is given by Smaller of ( Vshear , Vbearing ) (10) Japanese empirical equation for shear strength of a set of keys with joint reinforcement (Mochizuki et al) n m Vu = 0.1 fc' ∑ wi xi + ∑ a jσ y i =1 j =1 (11) 24 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Ductile connection 1) Beam hinging Beam top bars are arranged at site 25 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Ductile connection 1) Most popular and well established beam column arrangement in Japan Courtesy of Dr. Masaru Teraoka at Fujita Corporation26 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Ductile connection 2) Beam hinging Beam bottom bars are anchored in a joint with 90 degree hooks 27 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Ductile connection 2) Beam hinging 28 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Ductile connection 3) Beam hinging Continuous beam unit with beam-to-column joint 29 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Ductile connection 3) Beam unit is put on column One Directional Continuous Beam Unit Beam hinging 30 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Ductile connection 3) One Directional Continuous Beam Unit Beam-to-beam Joint Strong Joint Courtesy of Dr. Tsutomu Komuro at Taisei Corporation 31 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Ductile connection 3) Two Directional continuous Beam Unit Courtesy of Prof. Makoto Maruta at Kajima Corporation 32 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Ductile connection 3) Post tensioned precast prestressed beam 33 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Beam to Beam; Strong connection) Re-bar welding Casting concrete at site Shear key Courtesy of Dr. Masaru Teraoka at Fujita Corporation34 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Beam to Beam; Strong connection) Exterior surface of precast beam unit Casting concrete at site Mechanical cou pler Roughene d surface 35 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Beam to Beam; Strong connection) Grout outlet Only grout injection Grout injection Threaded splice No protruding re-bar 36 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Beam to Beam; Strong connection) Construction work 37 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of frame system (Connection Interface) Composite column section Inner surface is roughened Internal cross tie is buried in precast unit Composite Beam section Internal cross tie is placed at site Inner surface is roughened Bottom reinforcement is buried in precast unit Bottom reinforcement is placed at site 38 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of wall system (Wall-beam Unit + Column Unit + Cast-in-situ Concrete at Connections) Cast in Place Concrete 39 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of wall system Slab & beam reinforcemen t Mortar sleeve joint Cast-in-place part Cast-inp l a c e vertical joint Precas t column Lap splicing Cast-in-place part Panel’s hor. & v e r t . reinforcement G r o u t horizontal joint Integrated beam Story i Precast panel S h e a r key Cast-in-place part Courtesy of Dr. Hassane Ousalem at Takenaka Corporation 40 Cast-in-place part Story i+2 Cast-in-place beam-column joint and slab Story i+1 Mechanical s p l i c e device Precast Wall Panel + Precast Colum Unit + Cast-in-situ Beam Column Joint + Cast -in-situ Floor Slab Mainly for apartment buildings of middle rise height Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of Half Precast Slab System Top reinforcement: Enough buckling strength is required to prevent buckling during construction process. Truss bar: Slab shear and lateral stability of top reinforcement 41 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Part 1 - 4. Typical Detailing of Precast Connections Joint examples of Precast Prestressed Half Slab System Top Reinforcement Arranged at Site Top Reinforcement Arranged at Site Cast-in-situ Concrete Wire Mesh Precast Pre-tensioned Prestressed Concrete Unit Void Prestressing Strand Rough Surface 42 Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Precast and prestressed concrete Reinforced concrete Intermission Beautiful Historic Bridge in Switzerland Built in 1930 Good materials, careful detailing and affectionate construction 43