P. Benson Shing

Finite-Element Model Updating for Assessment of Progressive Damage in a 3-Story Infilled RC Frame

AbstractThis paper presents a study on the identification of progressive damage, using an equivalent linear finite-element model updating strategy, in a masonry infilled RC frame that was tested on a shake table. A two-thirds-scale, 3-story, 2-bay, infilled RC frame was tested on the UCSD–NEES shake table to investigate the seismic performance of this type of construction. The shake table tests induced damage in the structure progressively through scaled historical earthquake records of increasing intensity. Between the earthquake tests and at various levels of damage, low-amplitude white-noise base excitations were applied to the infilled RC frame. In this study, the effective modal parameters of the damaged structure have been identified from the white-noise test data with the assumption that it responded in a quasi-linear manner. Modal identification has been performed using a deterministic-stochastic subspace identification method based on the measured input–output data. A sensitivity-based finite-ele...

Cohesive Crack Model to Simulate Cyclic Response of Concrete and Masonry Structures

This paper describes a constitutive model that uses a discrete crack approach to simulate the fracture behavior of quasi-brittle materials under cyclic load reversals. Quasi-brittle materials include concrete and masonry. The propose model adopts a modified elasto-plastic formulation to simulate mixed-mode fracture, joint compaction, reversible shear dilatation, and crack opening and closing. The authors also develop a stress update algorithm to solve the nonlinear constitutive equations. The model has been implemented in a finite element program. Experimental data from material tests and structural subassembly tests conducted on reinforced concrete and unreinforced masonry structures confirm the validity of the proposed model.

Shake-Table Tests of a 3-Story Masonry-Infilled RC Frame Retrofitted with Composite Materials

AbstractThis paper presents a study that investigated the effectiveness of retrofitting unreinforced masonry infill walls with composite materials to enhance the seismic performance of infilled nonductile RC frames. The primary retrofit scheme considered was the use of engineered cementitious composite overlays. Shake-table tests were conducted on a 2/3-scale, 3-story, 2-bay, masonry infilled RC frame that had one bottom-story wall retrofitted with engineered cementitious composites. The influence of this retrofit on the performance of the structure was investigated using the experimental observations and results of nonlinear finite element analyses. Furthermore, after walls in the second story of the structure were damaged, they were repaired by injecting epoxy into cracked mortar joints, and strengthened with a glass-fiber reinforced polymer overlay. It has been shown that both retrofit schemes are effective in enhancing the seismic performance of the structure and preventing diagonal shear failures of ...

Seismic performance of non-ductile RC frames with brick infill

This paper summarizes some of the findings of a research project that investigates the seismic performance of masonry-infilled, non-ductile, RC frames, including the development of reliable analytical methods for performance assessment and effective retrofit techniques. Quasi-static tests were conducted on small and large-scale, single-story, single-bay, RC frames infilled with brick masonry walls with and without openings. Some of the infill walls were strengthened with an engineered cementitious composite material. Furthermore, two 2/3-scale, three-story, two-bay, masonry-infilled, RC frames were tested on a shake table. One was tested with no retrofit measures, and the other had infill walls strengthened with the engineered cementitious composite and fiber reinforced polymeric material in the first and second stories, respectively. The tests have demonstrated the effectiveness of the retrofit measures. Computation models that combine smeared and discrete cracks have been developed and validated by the experimental data. Some of the experimental and numerical results are presented in this paper.

Validation of a fast hybrid test system with substructure tests

This paper presents the substructure testing methodology developed for a state-of-the-art fast hybrid test system and the testing of a steel zipper frame. The testing technique is based on the pseudodynamic test concept that combines model-based simulation with physical testing. In the hybrid tests presented here, only the bottom-story braces of a three-story zipper frame were tested, while the rest of the frame was modeled in a computer during a test using a general structural analysis framework OpenSEES. The tests have demonstrated the capability and reliability of the system. The discussion also covers pertinent issues and considerations for carrying out a successful test.

Bond strength and cyclic bond deterioration of large-diameter bars

A study on the bond strength and cyclic bond deterioration of large diameter reinforcing bars embedded in well-confined concrete is presented. The study included monotonic pullout tests and cyclic pull-pull tests conducted on No. 11, No. 14, and No. 18 (36, 43, and 57 mm) reinforcing bars. The bond stress-slip relations obtained from the tests are presented, and the effects of the compressive strength of concrete, bar size, pull direction (for a vertically cast bar), and slip history on the bond strength are examined. Moreover, a phenomenological bond stress-slip law for monotonic and cyclic loading is proposed for bars embedded in well-confined concrete. This law has been validated with experimental results obtained in this study and in previous research.

Bond-Slip Model for Detailed Finite-Element Analysis of Reinforced Concrete Structures

A new interface model to simulate the bond-slip behavior of reinforcing bars is presented. The model adopts a semiempirical law to predict the bond stress-versus-slip relations of bars, accounting for the bond deterioration caused by cyclic slip reversals, the tensile yielding of the bars, and the splitting of concrete. The wedging action of the ribs is represented by assuming that the normal stress of the interface is proportional to the bond stress. The model has been implemented in a finite-element analysis program and has been validated with laboratory experiments that include monotonic and cyclic bond-slip and anchorage tests of bars with different embedment lengths and a test on an RC column subjected to cyclic lateral loading. The model is easy to calibrate and computationally efficient, and it accurately predicts the bond-slip behavior of bars embedded in well-confined concrete. It also simulates bond failure attributable to the splitting of concrete in an approximate manner.

Fragility Analysis of Reinforced Masonry Shear Walls

Fragility functions have been developed to evaluate the damageability of fully grouted and partially grouted reinforced masonry shear walls subjected to in-plane seismic loading. Six damage states are considered, representing different levels of flexure, diagonal shear, and sliding shear damage. For each damage state, two classes of fragility functions have been developed. One has the story-drift ratio as the demand parameter. The other uses normalized demand parameters that account for the specific loading condition and design details of a wall component. All the fragility functions are derived from experimental data except for those developed for partially grouted walls and the sliding shear damage state. With both classes of fragility functions, the seismic damageability of flexure-dominated cantilever reinforced masonry shear walls in a four-story building has been assessed. It has been shown that the normalized flexural demand parameter provides a better correlation to the degree of damage developed in a wall than the story-drift ratio.

Numerical Study of Masonry-Infilled RC Frames Retrofitted with ECC Overlays

AbstractThis paper presents a nonlinear finite-element modeling method to evaluate the seismic performance of reinforced concrete (RC) frames that have unreinforced masonry infill walls retrofitted with engineered cementitious composite (ECC) overlays. The method has been validated by results of shake-table tests conducted on a 2/3-scale, three-story, two-bay, infilled frame. Results of a numerical study conducted with the validated model have provided further insight into the performance of a structure retrofitted with this technique. A simplified analytical method to assess the shear capacity of an ECC overlay and determine the number and size of shear dowels required to prevent dowel failure has been proposed to ensure a more ductile behavior of the retrofitted structure. Results have shown that the performance of a retrofitted system can be greatly improved by preventing dowel failure so that the benefit of the ductile inelastic behavior of the ECC can be fully exploited. Furthermore, methods to estim...

Elastoplastic Dilatant Interface Model for Cyclic Bond-Slip Behavior of Reinforcing Bars

AbstractThis paper presents a new interface model to simulate the cyclic bond-slip behavior of steel reinforcing bars embedded in concrete. A multi-surface plasticity formulation is used to model two major inelastic deformation mechanisms occurring in bond slip. One is the crushing and shearing of the concrete between the bar ribs, and the other is the sliding between the concrete and bar surfaces. These two mechanisms are represented by different yield surfaces and nonassociated flow rules. The flow rules account for the shear dilatation of the interface induced by the wedging action of the bar ribs and crushed concrete particles. The interface model has been implemented in a finite element analysis program and has been validated with experimental data. The model is easy to calibrate and is able to reproduce the bond-slip behavior of bars under a wide range of confinement situations, including bar pullout and concrete splitting failures.