Professor Hiroshi Mutsuyoshi of Japan Prestressed Concrete Institute is co-moderating a special session will focused on the recent advancement of prestressed concrete for bridges and structures using conventional and nonconventional materials. Presentations and technical papers will include the conceptual development of innovative prestressed concrete, laboratory experiments, numerical modeling, and case studies. State-of-the-art prestressing techniques and nonconventional materials such as fiber reinforced polymer (FRP) composites to address the sustainable performance of concrete members will also be considered. The session will benefit practicing engineers, government officials, and academics.
1) Review the importance of non-conventional materials for bridge girders;
(2) Identify structural demand for prestressed bridge girders;
(3) Recognize the use of emerging materials in precast application;
(4) Develop new concepts for concrete bridge design.
Prestressed Concrete using Calcium Sulfoaluminate Cement
Presented By: Cameron Murray
Affiliation: University of Arkansas
Description: Calcium Sulfoaluminate-Belite (CSA) cement is a hydraulic cement which sets rapidly and gains strength very quickly. With CSA cement, strengths of 4 ksi in as little as 2 hours are possible under many environmental conditions with no steam curing. The dimensional stability of CSA cement concrete is also superior to portland cement. These advantages make CSA cement an enticing material for precast-prestressed concrete. This talk reviews ongoing research on CSA cement for prestressed concrete beams. The authors have cast prestressed concrete beams using CSA cement at commercial precast facilities and in a lab setting. These studies have shown that it is feasible to release prestress in 2-4 hours using CSA cement, and that many properties of these beams are at least as good, if not better than portland cement. Transfer lengths, development lengths, flexural strengths, and prestress losses were measured in these studies. Despite some unique difficulties of working with a rapid setting product, prestress force was released in as little as two hours with no adverse effects. The properties of the beams will be reviewed in this talk to highlight the potential of this material for precast prestressed construction.
Impact of Void Details on the Performance of Hollow Pretensioned Concrete Bent Caps
Presented By: Codi McKee
Affiliation: Texas AM University College Station
Description: While precast bent caps can be of significant benefit for accelerated bridge construction, weight can become a limiting factor for wide bridges. Pretensioned bent caps with interior voids for weight reduction offer an attractive alternative. Subassemblies of hollow pretensioned concrete bent caps, including the column and connection region without an interior void, were tested to allow for examination of the performance of voids within a multi-column substructure. The location of void termination was varied to assess the impact on development of cracks and failure mechanisms. To better assess these, a grid of LED targets was used to measure displacements in the void termination region. Readings were used to infer strains. Evaluation of principal tensile strains correlate to observed crack damage and the regions of largest principal compressive strains indicate the regions of the bent caps where failure ultimately occurs. Collected data can be used for the validation of numerical models to further assess void details on the performance of hollow prestressed concrete beams.
Distributed Horizontal Shear Reinforcement to Mitigate Shear Failures at End Regions of Pretensioned Beams
Presented By: Bruce Russell
Affiliation: Oklahoma State University
Description: In the 1994 Northridge Earthquake, precast, prestressed double tees and inverted tees suffered collapse caused by larger than normal vertical accelerations, and the resulting high internal shears that were applied to the members. The episode highlighted the need to provide additional anchorage for the longitudinal tension forces necessary to resist shear forces at or very near the support for pretensioned members. The smooth nature of prestressing strands and its lack of mechanical anchorage can present problems in shear. The smooth wire strands struggle to develop adequate anchorage near end regions where development of tension capacity is not assured. The research presented shows that cracking in end regions can be mitigated by distributing longitudinal mild reinforcement within narrow webs and stems of precast, prestressed concrete beams. By limiting the propagation of shear cracks, the reinforcement also mitigates damage to the anchorage zone and thus improves the strands’ ability to develop tension forces near the end of the member. Additionally, alternative load paths are provided which enable re-distribution of the shear deformations and allows alternative load paths for shear forces. Shear vs. strain relationships, similar to the modified compression field theory are developed based on measurements from testing, which can provide a rational basis for design. Alternatively, analysis techniques that focus on variations of strut and tie modeling are described. These are also discussed in terms of design techniques.
Field Deployment of CFCC in Highway Bridge Applications
Presented By: Yoshiaki Yamamoto
Affiliation: Tokyo Rope Mfg Co.
Description: Applications of Carbon Fiber Composite Cable (CFCC) will be presented for highway bridges.
Crack Development and Energy Absorption of Cementitious Composite Reinforced by Polypropylene and Cold-Drawn Shaved Steel Fiber for Prestressed Concrete Application
Presented By: Samad Gharehdaghi
Affiliation: University of Nevada, Las Vegas
Description: Over the last century, concrete has continuously developed to enhance all aspects of engineering properties. Those efforts resulted in creating three main classes of concrete: High Strength, High Performance, and Ultra-High-Performance Concrete. Despite enhancement of engineering properties, brittleness and low toughness are still two concrete weaknesses in prestressed concrete. Mixing the concrete with fibers, including synthetic and natural, is an effective method to address both problems. In this research, the water-cement ratios of 0.4 and 1.0% by volume of steel fibers and polypropylene are utilized to make the cementitious composite matrix. The main objective of this research is to investigate the effect of adding cold-drown shaved steel fiber and polypropylene fiber on energy absorption of the cementitious composite under drop-weight impact test. Among several methods of impact test, two velocity-based impact tests are classified in low velocity (quasi-static) test and high velocity (dynamic) test. Drop-weight test is one of low-velocity impact tests in which the velocity of the striking body is lower than 10 m/s. The energy absorption of cementitious composite reinforced with steel fiber and polypropylene fiber are measured and compared. Investigation of cementitious composite incorporating steel fiber indicated improvement in brittleness throughout changing radial to diagonal failure mechanism. The outstanding performance of synthetic fiber reinforcement decreased crack propagation and debris spatter specimen subjected to impact load.
Long-term Deflections of Beams and Flat Plates: Control by Post-tensioning
Presented By: Amin Ghali
Affiliation: University of Calgary
Description: Probable long-term deflection of beams and flat plates is predicted by analysis based on equilibrium and compatibility. The effect of cracking, creep and shrinkage of concrete and relaxation of prestressed reinforcement is considered. Material parameters for elasticity modulus, tensile strength, creep and shrinkage of concrete and relaxation of prestressed reinforcement are among the input data. The effect of cracking, induced by transient loading on long-term deflection, is considered. The analysis applicable to beams is extended to flat plates idealized as grids. The long-term deflection of a flat plate panel is controlled to a desired level by the design of post-tensioning forces.