This paper describes a methodology to optimize cost and CO2 emissions when designing precast–prestressed concrete road bridges with a double U-shape cross-section. To this end, a hybrid glowworm ...swarm optimization algorithm (SAGSO) is used to combine the synergy effect of the local search with simulated annealing (SA) and the global search with glowworm swarm optimization (GSO). The solution is defined by 40 variables, including the geometry, materials and reinforcement of the beam and the slab. Regarding the material, high strength concrete is used as well as self-compacting concrete in beams. Results provide engineers with useful guidelines to design PC precast bridges. The analysis also revealed that reducing costs by 1 Euro can save up to 1.75kg in CO2 emissions. Finally, the parametric study indicates that optimal solutions in terms of monetary costs have quite a satisfactory environmental outcome and differ only slightly from the best possible environmental solution obtained.
•A methodology to optimize CO2 emissions when designing PC precast road is proposed.•A new hybrid glowworm swarm optimization algorithm (SAGSO) is described.•Optimal cost solutions have quite a satisfactory environmental outcome when using high strength and self-compacting concrete.•The study is adjustable to the constraints and particular needs of realistic projects.
•Study on hybrid connections of precast concrete.•Steel bars yielding of PC beams were not achieved in the critical section.•The performance of PC2 significantly improved due to stiffening of the ...steel angles.•RC and PC2 specimens failed in flexural and PC1 failed at the steel plate yielding.•Concrete crushed did not occur in the PC specimens.
In general, precast concrete structure has insufficient ductility to resist seismic load. Detailed understanding on the behaviour of precast concrete connections are limited and current researches are focused addressing this. In this study, two precast and two monolithic concrete joints for exterior beam-to-column connection were tested under cyclic loading. The installation of precast specimens was prepared using dry type method while the monolithic joints were casted in-situ. The evaluation of seismic performance of the joints was conducted by applying hysteretic reverse cyclic loading until failure. Information regarding the strength, ductility and stiffness properties of the connection were recorded and analysed. Based on the test results and damage condition, the initial design of the joint was improved. Consequently, a new joint was constructed and tested, which exhibited a better performance. Precast concrete connections showed stable load–displacement cycles and dissipated a higher energy. The structural drift obtained was up to 9.0%. Pinching and deterioration were attained at a drift ratio of 4.5%. Also, there was improvement in the tested precast joints based on deflection, plastic hinges, crack pattern and shear deformation. Thus, the precast joints had a satisfactory resistance to seismic loads.
•An innovative hybrid beam-column connection is proposed for precast concrete structures.•The seismic behavior of the proposed connection is experimentally and numerically studied.•A small-scale ...parametric study is organized to study the parameters related to the HBC connection.
Precast concrete structures have become a popular option among available structural forms for their superior mechanical characteristics, economy and sustainable development as well as architectural versatility. However, some technical problem such as complex load path, uncertainty of structural stiffness of beam-column joints and inconvenience for disassembly hinders the application and development of precast concrete structures. In this study, an innovative hybrid beam-column connection is proposed with hierarchy of strong connection and weak structural members for precast concrete structures. An experimental and numerical study is organized to study the seismic behavior of the proposed connection including hysteretic curves, skeleton curves and dissipation capacity. The experimental results showed that the new hybrid beam-column connection can reduce the stress concentration effect at the joint and achieve comparable mechanical performance with cast-in-site connections. A numerical investigation on the seismic behavior of the hybrid beam-column connection is carried out. The benchmark models are initially created and validated against the test data and after that a small-scale parametric study is organized. The effect of the position of I-sectional connector (d), the length of cladding plates (l) and axial compression ratio (α) on seismic behavior of the hybrid beam-column connection is investigated and analyzed.
•Defect-free grouted sleeve wall panels were equivalent to monolithic-cast walls having continuous bars.•Grout sleeve defects adversely affect wall behavior – primarily when the spliced bar is in ...tension.•The degree of the defect impacts the force the bar can develop.•Panels that achieved at least 92% of their capacity were indistinguishable from defect-free panels.•Noticeable loss of performance was evident at wall panel capacities of 85% and lower.
Precast concrete wall systems are effective means of resisting seismic forces in many structures. However, their performance is affected by the ability to properly connect elements – usually with grout sleeves. Grout sleeve connections are known to be susceptible to backflow during grouting resulting in partially grouted or occasionally entirely ungrouted sleeves. In this study an investigation of the impact of sleeve grouting defects on the seismic performance of precast concrete shear walls is presented. Grouting defects of different sizes and at different positions in the walls were intentionally introduced. Reversed cyclic loading tests of precast concrete shear wall specimens and a comparable monolithically cast-in-place concrete shear wall specimen were performed. The defect-free grouted sleeve panels were shown to be equivalent to monolithic cast walls having continuous bars in terms of capacity although, due to the short sleeve embedment, the precast walls are less stiff and therefore demonstrate reduced ductility. Energy dissipation, however is similar and both monolithically cast and precast walls meet the requirements for use as seismic resistant systems. The study showed that grout sleeve defects adversely affect wall behavior – primarily when the spliced bar is in tension. The impact of defects can be assessed through standard design equations by assuming that the degree of the defect impacts the force the bar can develop. As demonstrated in this study, wall performance becomes an issue of quantifying and predicting defects and their effect, not on the individual bars, but on the wall panel assembly. The panels in this study were dominated by flexural behavior; thus the reduction in panel moment capacity provides a means of differentiating behavior. Panels that maintained at least 92% of their theoretical flexure capacity were mostly indistinguishable from defect-free panels. Noticeable loss of performance was evident at panel capacities of 85% and lower.
•The paper proposed the rebar lapping in grout-filled constrained hole connection.•The seismic behavior of precast concrete shear wall with horizontal joint is studied.•The precast concrete shear ...walls can be equivalent to cast-in-place design.
In this paper, the seismic behaviors of four precast shear wall specimens and one cast-in-place shear wall specimen are investigated by pseudo-static test method. For the precast shear wall specimens, a new type of assembled rebar lap splices with prepared grout-filled holes and constraining spiral hoops were applied. Different vertical rebar lap splice positions and different rebar lap lengths at the horizontal assembly joints of the precast specimens were designed and fabricated in order to compare their seismic behaviors with the cast-in-place specimen. The geometric size and rebars of four precast specimens are totally same as those of the cast-in-place specimen. By analysis of test results including the load-lateral drift hysteresis curves, crack propagation and rebar strains, the failure modes, bearing capacity, hysteretic characteristics, ductility, rigidity degeneration and energy dissipation of all specimens were obtained and compared. The test results show that the precast concrete shear walls with horizontal assembly joints by this kind of rebar connection have good seismic behaviors and could be equivalent to the cast-in-place shear walls on the conditions of specified construction details.
•Very limited study on the PC beam under impact is available.•Numerical model of PC beam under impact is verified by testing data.•Effect of slight inclination angle of drop weight on structural ...response of PC beam is disclosed.•Effects of interface and grout sleeve on the impact resistance performance are studied.•Failure mode, impact force and structural response of PC and RC beams subjected to impact loads are compared.
Precast concrete (PC) structures are increasingly employed in recent years due to their advantages in better construction quality control and saving construction time. Most of the existing researches have been carried out to study the seismic performance of PC structures. The investigation of PC beams with wet connection under impact loads is, however, very limited in open literature. In this paper, numerical studies are conducted to investigate the dynamic behavior of PC beams with wet connections subjected to impact loads by LS-DYNA. The numerical models are calibrated with the experimental results from other researchers. With the calibrated numerical model, the dynamic performance of PC beams is compared with that of monolithic RC beams. It is found that the impact forces on PC and RC beams are similar due to the identical contact stiffness at the impact location. However, the interfaces between PC components and cast-in-place concrete (CIPC) components as well as grout sleeves used to connect longitudinal rebars cause uneven stiffness distributions of PC beams, hence resulting in different failure modes of PC and RC beams. Parametric studies are conducted to investigate the effects of three parameters, i.e., impact energy with respect to impact mass and velocity, inclination angle of the drop weight, and concrete strength on the dynamic response of PC beams subjected to impact loads. The results obtained in this research shine some lights on the impact performances of PC beams.
AbstractTo satisfy the easy-repair demands of precast concrete (PC) frames after an earthquake, a PC frame with replaceable artificial controllable plastic hinges (ACPHs) is proposed in this paper. ...ACPHs were installed at each beam end on both sides of the frame, which concentrated the structural deformation to avoid any damage of precast reinforced concrete members. In this study, to explore the seismic behavior and ACPH location factor on the seismic performance of the frame structures, cyclic loading tests were conducted on two precast concrete frames with different positionings of the ACPH and cast-in-situ frame. The test results indicate that the ACPH frame exhibited favorable seismic performance, and the bearing capacity and energy dissipation capacity can be improved by appropriately extending the distance from the ACPH to the cylinder. Based on the principle of maximizing the elastic range resistance of precast reinforced concrete beams, the formulas for calculating the optimal locations of ACPHs were established.
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•Simulation of segmental columns subjected to vehicle collision.•New simulation for prestressing structures.•Impact behavior of segmental columns.•Effects of critical parameters on ...the impact behavior.
This study numerically investigates the response of precast concrete segmental columns with unbonded prestress tendons subjected to vehicle collision. Numerical models are developed using LS-DYNA and validated against experimental tests. The validated model is then used to perform intensive numerical simulations to analyze the effectiveness of prestressing level, number of segments, concrete strength, and vehicle velocity on the behavior of precast segmental concrete columns. The numerical results have shown that the effect of the initial prestressing level and the number of segments are marginal on the impact force time history but significant on the residual displacement and the damage of the column. Better self-centering capacity as well as smaller lateral displacement can be achieved on segmental columns by reducing the number of column segments and increasing the prestress level. In addition, the height-to-depth ratio of a concrete segment should be smaller than two in order to minimize an undesirable local damage at the rear side opposite the impact point. Varying concrete strength from 20 MPa to 80 MPa shows an unnoticeable change of the impact force but its effects on mitigating the damage of the columns are considerable. Last but not least, increasing the impact velocity does not always increase the peak impact force of a segmental column. It is recommended that both the peak impact force and impulse should be taken into consideration in the analysis and design of segmental columns against vehicle impact.
Siliceous fly ash (FA) is the main additive to currently produced concretes. The utilization of this industrial waste carries an evident pro-ecological factor. In addition, such actions have a ...positive effect on the structure and mechanical parameters of mature concrete. Unfortunately, the problem of using FA as a Portland cement replacement is that it significantly reduces the performance of concretes in the early stages of their curing. This limits the possibility of using this type of concrete, e.g., in prefabrication, where it is required to obtain high-strength composites after short periods of curing. In order to minimize these negative effects, this research was undertaken to increase the early strength of concretes with FA through the application of a specifically formulated chemical nano-admixture (NA) in the form of seeds of the C-S-H phase. The NA was used to accelerate the strength growth in concretes. Therefore, this paper presents results of tests of modified concretes both with the addition of FA and with innovative NA. The analyses were carried out based on the results of the macroscopic and microstructural tests in five time periods, i.e., after 4, 8, 12, 24 and 72 h. The results of tests carried out with the use of NA clearly indicate the possibility of using FA in a wide range of management areas in sustainable concrete prefabrication.
Recent earthquakes have demonstrated that reinforced concrete (RC) frames, which form a beam‐sway mechanism, sustain damage to beams and floors that can be particularly difficult and costly to ...repair. This paper proposes a new structural system, which combines RC frames with precast concrete spreader‐walls. The spreader‐walls are fixed to frames with connections that allow them to pivot and are carefully arranged so that they distribute seismic deformation demands over the building height. This in turn allows the designer to force plastic hinges to occur at column ends without the risk of a soft‐story mechanism forming and without costly damage to beams and floors. Nonlinear time history analyses of two sets of 4‐, 8‐, and 12‐story buildings are conducted with and without the spreader‐walls. The analyses show that the system behaves as intended and has the potential to enhance the reparability of RC frame structures. To this end, experimental research is recommended to ensure that the proposed connection details behave as desired prior to their implementation in practice.
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