153 publications from this institution
No abstract is provided for this article.
No abstract is provided for this article.
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Progressive collapse behavior of RC infilled frames is studied experimentally under quasi-static loading and numerically by using macro (strut) and micro (finite-element) models to simulate the damage propagation within infill walls. A three-strut model is proposed to simulate the overall behavior of infill walls based on the observation that corner regions of infill walls play an important role even after the cracking of the diagonal region in infill walls. The proposed three-strut model is implemented using commercially available software. The accuracy of the proposed method is evaluated by comparing the experimental data with simulated responses from detailed finite-element models and simplified strut models. The modified three-strut model is also compared with other widely used strut models. The comparison shows that the proposed three-strut model predicts the maximum resistance force with higher accuracy. Finally, a simpler model is developed based on the proposed three-strut model for infill walls. This simpler model can easily be implemented by practicing engineers to predict the overall behavior of the infilled frame with acceptable accuracy.
Little research is reported on the properties of Portland cement concrete (PCC) mixtures comprising plastic waste materials. Therefore, this novel study was initiated to evaluate the effects of plastic waste materials on different properties of PCC. Plastic boxes and containers made of polypropylene were cut, grinded, pulverized, and incorporated into PCC mixtures. Sand was partially replaced by plastic waste materials with 0%, 5%, 10%, 15%, and 20% volume ratios. Experiments were conducted using PCC cylinders and prisms to evaluate several unique properties of PCC containing plastic waste. Innovative interactions and contributions of several PCC properties including workability, air content, density, water absorption, mechanical properties, rapid chloride ion penetration, and freeze–thaw deterioration are investigated. The new experimental data indicated that the workability and density of PCC decreased with increasing plastic waste replacement levels. The maximum decreases in workability and density were 23% and 6.2% for the PCC with 20% plastic replacement, respectively. On the other hand, our research has shown that air content and water absorption of PCC increases with increasing plastic waste amount. The maximum increase in air content and water absorption were 78% and 29% for the PCC with 20% plastic waste. This study also shows that the mechanical properties of PCC (e.g., compressive and splitting strengths) after 7 and 28 days of moist curing decreased with increasing plastic waste content. Another new finding is that the rapid chloride permeability of PCC increased and the freeze–thaw durability of PCC decreased with an increase in plastic waste amount. One of the most critical discoveries of this experimental study is that plastic waste increases the durability of PCC, i.e., durability factor of PCC with 20% plastic waste was 9.3% compared to 28.5% for the control PCC without plastic waste materials.
Structural behavior and corrosion resistance of hybrid fiber reinforced polymer (FRP) wrapped steel bars is investigated for use in reinforced concrete structures. Experiments were conducted in the laboratory to assess the axial tensile capacity and corrosion resistance of the composite bars, and flexural behavior of beams reinforced with these hybrid bars. Data from short term and long-term corrosion experiments were used to evaluate the resistance to degradation provided by the FRP, including applied defects to determine any gain in corrosion resistance over standard epoxy-coated bars. Corrosion experiments are performed by placing bars with and without applied defects in an aggressive solution that mimics a concrete pore environment. Corrosion rates of standard epoxy-coated bars and hybrid carbon and glass FRP wrapped steel bars were compared considering the crevice corrosion at applied defects. In addition to their contributions to the strength capacity of steel bars confirmed by the tensile tests, FRP-wrapped steel reinforcing bars have high corrosion resistance. The overall behavior of beams reinforced with hybrid FRP-steel bars was similar to those reinforced with epoxy coated bars. During the experiments, no debonding was observed between the hybrid bars and concrete inside the beams before failure.
Three exterior reinforced concrete beam-column joint specimens were tested under reverse cyclic loading. The joint region of these specimens suffered significant damage, whereas limited damage was observed in the beams. The damaged specimens were repaired and strengthened to prevent shear damage and strength deterioration inside the joint region and to achieve more ductile response. First, the damaged loose concrete was removed and replaced by high-strength nonshrink mortar. Then, fiber-reinforced polymer (FRP) strips were diagonally wrapped over the joint region, and longitudinal FRP strips were applied and anchored on the beams. The original strength was restored in all strengthened specimens under the application of the same loading history. Deformation capacities of the strengthened specimens were much larger than those of the original specimens.
Recent devastating earthquakes around the world have shown the vulnerability and deficiencies of existing reinforced concrete (RC) frame structures.In particular, recent research on seismic risk analysis have highlighted that nonductile concrete frame structures are much more susceptible to collapse than modern code-conforming frames.Therefore, for this type of structures, it is necessary to accurately model materials and members to capture the flexure, shear and flexure-shear failure modes in members and the potential collapse of the structure.In this paper, alternative retrofit methods are evaluated for these older frame buildings using a nonlinear structural performance assessment methodology.As a case study, the longitudinal frame of an existing building is modeled, including the effect of flexural-shearaxial load interaction and the bar slip deformational component in order to be able to capture column shear and axial failures.A probability-based framework is implemented in order to assess the structural performance and safety at each chosen performance level.This study shows that it is crucial to choose the most effective retrofit strategy based on the assessed performance of the bare frame.
Reinforced concrete buildings suffered significant damage in the region affected by the 29 May 2011 earthquake in Simav (Kutahya), Turkey. Typical building damage is classified and potential causes of damage are investigated. Reinforced concrete moment resisting frames with hollow brick infill walls are the most common structural system in and around the Simav city center while masonry construction is common in rural areas. Although the Simav earthquake, with a magnitude of 5.7 to 5.9, can be classified as a moderate earthquake, many buildings experienced damage varying from frequent diagonal cracking and brittle failure of infill walls to collapse or severe damage to frames due to short columns, soft stories or other reasons including insufficient or poor detailing of reinforcement. This study investigates and presents the seismicity of the region, characteristics of the measured ground motions, seismic load demands including response spectra, and damage mechanisms, potential causes and classification of observed damage in reinforced concrete buildings.
Insufficient or deteriorating reinforced-concrete piers in many existing bridges are required to be strengthened using economical, fast, and efficient methods. Currently, only a few methods can be used to strengthen circular columns. Steel jackets and fiber-reinforced polymer (FRP) composites are the two commonly used methods. In this study, along with these two strengthening methods, concrete jackets reinforced with spiral rebar, welded wire fabric (WWF), and a new steel reinforcement called PCS are investigated under different axial-load applications. Fifteen identical specimens were constructed, strengthened, and tested: one column with no strengthening; three columns strengthened with FRP; two with steel jacketing; and nine with concrete jacketing (two with WWF, three with spiral rebar, and four with the new reinforcement). The bare or unretrofitted specimens had a 152 mm (6 in.) diameter, while the outside diameter of concrete-jacketed specimens was 254 mm (10 in.). Effectiveness of each strengthening method in increasing the stiffness, axial capacity, and displacement ductility was investigated using the experimental data.
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Prefabricated 3D modules are widely adopted in building construction for better quality, lower demand on labor and construction space, faster construction, and less emission. Various types of modular structures and connections have been tested and are commercially available. A large number of actual applications demonstrate that the structural system of a modular building can be flexibly organized to suit for the topmost utility architecturally. However, in terms of the stability of the structural system, the role of prefabricated modules widely varies. A systematic summary and categorization of different structural stability systems and layout patterns, especially in multi-story modular buildings where load sharing and transfer between the units are necessary, has yet to be made. This paper provides a state-of-the-art review which focuses on four major structural aspects, e.g., module connection, individual module structure, layout pattern, and additional stability unit. Recommended combinations of structural parts of the system are provided. Nonlinear static or pushover analysis is carried out with the numerical model based on available experimental data to demonstrate the roles of individual modules and additional stability units on system stability. A rating procedure for the modular structural system is proposed to briefly evaluate several aspects of the multi-story modular building structures. Trends in design and usage of modular structure systems are presented using examples of 20 unique applications.
In different high seismic regions around the world, post-earthquake reconnaissance has shown that nonductile concrete frame structures are much more susceptible to collapse than modern code-conforming frames. Therefore, for this type of structures, it is necessary to accurately model materials and members to capture the flexure, shear, and flexure-shear failure modes in members and the potential collapse of the structure. In this paper, alternative retrofit methods are evaluated for these older frame buildings using a probability-based framework, based on nonlinear dynamic cloud analysis, in order to assess the structural performance and safety at each chosen performance level. As a case study, the longitudinal frame of an existing building is modeled, including the effect of flexural-shear-axial load interaction and the longitudinal bar slip deformation component in order to be able to capture column shear and axial failures. The critical demand to capacity ratio, corresponding to the component or mechanism that leads the structure closest to the onset of limit state (e.g., near collapse), is adopted as the structural response parameter. This structural response parameter, that is equal to unity at the onset of limit state, can encompass both ductile and brittle failure mechanisms. It can also register a possible shift in the governing failure mechanism with increasing intensity. Finally, the estimates of expected life cycle cost are compared for the retrofit methods considered in this research.
