Ahmad A. Hamid

In-Plane Behavior of Partially Grouted Reinforced Concrete Masonry Shear Walls

The objectives of this research were to experimentally establish the in-plane behavior of partially grouted (PG) reinforced concrete masonry shear walls and to assess the appropriateness of current seismic design provisions for such walls. To accomplish these, four PG special reinforced masonry shear walls (SRMSWs) were constructed based on the provisions of the Masonry Standards Joint Committee (MSJC) code and subjected to in-plane reversed cyclic displacements. The experimental test variables included mortar formulation, level of axial stress, and boundary conditions. The results of this study indicate that PG masonry shear walls respond similar to in-filled frames and provide little coupling between vertical reinforcing steels. Using these results along with those from past research, it is shown that the shear strength expression for reinforced masonry shear walls provided by MSJC (along with others) appears unconservative for PG masonry shear walls. In terms of displacement ductility, the results indicate that the response of PG SRMSW is consistent with the R factors provided by the 2006 International Building Code due to the required capacity design and increased shear demand provisions of the MSJC.

A data fusion approach for progressive damage quantification in reinforced concrete masonry walls

This paper presents a data fusion approach based on digital image correlation (DIC) and acoustic emission (AE) to detect, monitor and quantify progressive damage development in reinforced concrete masonry walls (CMW) with varying types of reinforcements. CMW were tested to evaluate their structural behavior under cyclic loading. The combination of DIC with AE provided a framework for the cross-correlation of full field strain maps on the surface of CMW with volume-inspecting acoustic activity. AE allowed in situ monitoring of damage progression which was correlated with the DIC through quantification of strain concentrations and by tracking crack evolution, visually verified. The presented results further demonstrate the relationships between the onset and development of cracking with changes in energy dissipation at each loading cycle, measured principal strains and computed AE energy, providing a promising paradigm for structural health monitoring applications on full-scale concrete masonry buildings.

Flexural Behavior of Reinforced Concrete Masonry Wallsunder Out-of-Plane Monotonic Loads

This paper presents the test results of an investigation carried out to study the behavior and flexural strength of vertically spanned reinforced concrete block masonry walls under out-of-plane monotonic loading. The study presented in this paper, which is part of the U.S.-Japan Coordinated Program on Masonry Building Research, addresses the elastic and inelastic behavior of reinforced block masonry walls. Six walls were tested to determine the effects of percentage and location of vertical reinforcement, block size, and extent of grouting. The behavior included cracking patterns and cracking moments, load-deflection curves up to and beyond the peak load, and displacement ductility. Test results showed that the percentage and location of vertical steel (centrally located versus staggered) had a significant effect on wall load-deflection curves, strength, and ductility. The extent of grouting (partially versus fully grouted) affected cracking load and consequently, flexural rigidity and deflection under service loads. The extent of grouting, however, did not show an adverse effect on wall stability in the inelastic range. The specified value of the modulus of rupture in the UBC-94 code is much lower than the experimental values of maximum tensile stress at first crack obtained for fully grouted walls. The theoretical analysis for the ultimate strength based on the Whitney stress block method that is included in the UBC-94 code showed a good correlation with the experimental results. Displacement ductility ratios ranged from 1.79 for the wall with 0.44 percent vertical steel to 16 for the wall with 0.19 percent steel. As expected, the displacement ductility of the wall panels decreased as the percentage of vertical reinforcement increased.

Acoustics and temperature based NDT for damage assessment of concrete masonry system subjected to cyclic loading

This paper represents a hybrid non-destructive testing (HNDT) approach based on infrared thermography (IRT), acoustic emission (AE) and ultrasonic (UT) techniques for effective damage quantification of partially grouted concrete masonry walls (CMW). This integrated approach has the potential to be implemented for the health monitoring of concrete masonry systems. The implementation of this hybrid approach assists the cross validation of in situ recorded information for structural damage assessment. In this context, NDT was performed on a set of partially grouted CMW subjected to cyclic loading. Acoustic emission (AE) signals and Infrared thermography (IRT) images were recorded during each cycle of loading while the ultrasonic (UT) tests were performed in between each loading cycle. Four accelerometers, bonded at the toe of the wall, were used for recording waveforms for both passive (AE) and active (UT) acoustics. For the active approach, high frequency stress waves were generated by an instrumented hammer and the corresponding waveforms were recorded by the accelerometers. The obtained AE, IRT, and UT results were correlated to visually confirm accumulated progressive damage throughout the loading history. Detailed post-processing of these results was performed to characterize the defects at the region of interest. The obtained experimental results demonstrated the potential of the methods to detect flaws on monitored specimens; further experimental investigations are planned towards the quantitative use of these NDT methods.

FLEXURAL BEHAVIOR OF JOINT REINFORCED BLOCK MASONRY WALLS

This paper presents an experimental study of the behavior of horizontally spanning joint reinforced block masonry walls under out-of-plane monotonic lateral loading. Five full-scale wall panels were tested to determine the effect of amount and type of horizontal steel and bond pattern (running versus stack bond) on wall behavior including cracking moment, load deflection relationships, and flexural strength. Correlation between flexural strength test results and the UBC-88 code strength design method is presented. The results show that the shape of the load deflection curve was a function of the spacing and type of reinforcement. Details of the results are presented and discussed. It is concluded that as the UBC strength design method gives a reasonable estimate of wall flexural strength, a method based on strain compatibility would provide more accurate results.

New Design Detail to Enhance the Seismic Performance of Ordinary Reinforced Partially Grouted Masonry Structures

AbstractRecent studies have shown that in the event of a strong earthquake, partially grouted (PG) masonry walls would most likely not perform according to code expectations. The research reported herein is focused on introducing an economically competitive design detail to enhance the seismic performance and safety index of PG reinforced masonry shear walls. Besides the conventional design details of single grouted vertical cells with single bond beams, two other details called double grouted vertical cells with double bond beams, and double grouted vertical cells with single bond beams plus joint reinforcement, were constructed and tested in this study. Test results demonstrated that the single grouted wall failed in a low ductility shear-dominated mode, while the modified design details resulted in a change to the high ductility shear failure mode. Results of nonlinear static and incremental dynamic analyses showed that using the proposed enhanced detail can significantly improve the seismic performanc...

Seismic Evaluation of an Elevated Highway Bridge in a Low Seismic Region - a Case Study

This paper presents the results of the seismic evaluation of an elevated seven-span bridge with tall piers in western Pennsylvania. The bridge was modeled using the SEISAB software, and the analysis used modal superposition method. Various modeling strategies related to piers, abutments, expansion joints, fixed joints, rocker bearings, and hanger supports were studied. Several modeling options were made to capture different behavior responses under seismic loading conditions. The force and displacement demands are compared, and an assessment is made with respect to the potential for damage based on the analysis results. The result of the study shows that for the level of earthquakes expected in the region, columns will not be overstressed. Furthermore, the analysis results show that displacements of the superstructure should not be of concern in light of the fact that there is sufficient bearing seat width and that concrete pedestals have been added in front of the bearing supports to presumably prevent the walking off of the bearing from the support. The study concludes that considering the low level of earthquakes expected in PA, the potential for collapse of the superstructure due to bearing support failure is negligible. The paper contributes to better understanding of the behavior of tall and elevated highway bridges in low seismic regions. The results of the study reinforce the view that decisions on seismic retrofit of such bridges in low seismic regions should not be based on column tie spacing.

Thermal Energy Performance of Load-Bearing Concrete Masonry in Residential Buildings in Hot, Dry Climates

Abstract This paper addresses the thermal performance of load-bearing concrete masonry wall assemblies for residential application under hot, dry climatic conditions. A comparative study between the thermal response of conventional infilled frame construction and load-bearing masonry construction is performed. Both construction types are thermally modeled using a computer simulation technique in which a dynamic thermal analysis is performed, taking into account pertinent physical characteristics including the thermal mass of building materials. Hourly weather data representative of hot, dry climatic conditions are employed to simulate hourly indoor temperature levels. The results are analyzed in light of current thermal comfort assessments and show that load-bearing concrete masonry walls exhibit thermal qualities that are generally superior to those exhibited by conventional infilled reinforced concrete frame with brick masonry. It is therefore concluded that the use of load-bearing concrete masonry wall...

Damage detection of concrete masonry structures by enhancing deformation measurement using DIC

This study focuses on deformability and damage detection of a concrete masonry wall. It employed point-to-point traditional strain gages and full-field measurement technique using digital image correlation (DIC) to investigate the damage and deformability of a partially grouted (PG) reinforced masonry wall. A set of ungrouted and grouted assemblages and full-scale concrete masonry shear wall were constructed and tested under displacement control loading. The wall was constructed according with masonry standards joint committee (MSJC 2013) and tested under constant vertical compression load and horizontal lateral load using quasi-static displacement procedure. The DIC method was used to determine non-uniform strain contours on the assemblages. This method was verified by comparing strains along the selected directions with traditional TML gage results. After a successful comparison, the method was used to investigate the state of damage and deformability of the wall specimen. Panel deformation, crack pattern, displacement at the top, and the base strain of the wall were captured using full-field measurement and results were in a good agreement with traditional strain gages. It is concluded that full-filed measurements using DIC is promising especially when the test specimens experience inelastic deformation and high degree of damage. The ability to characterize and anticipate failure mechanisms of concrete masonry systems by depicting strain distribution, categorizing structural cracks and investigating their effects on the behavior of the wall were also shown using DIC. In addition to monitoring strains across the gage length, the DIC method provided full-field strain behavior of the test specimens and revealed strain hotspots at locations that corresponded to failure.

Nonlinear analysis techniques of block masonry walls in nuclear power plants

Abstract Concrete masonry walls have been used extensively in nuclear power plants as non-load bearing partitions serving as pipe supports, fire walls, radiation shielding barriers, and similar heavy construction separations. When subjected to earthquake loads, these walls should maintain their structural integrity. However, some of the walls do not meet design requirements based on working stress allowables. Consequently, utilities have used non-linear analysis techniques, such as the arching theory and the energy balance technique, to qualify such walls. This paper presents a critical review of the applicability of non-linear analysis techniques for both unreinforced and reinforced block masonry walls under seismic loading. These techniques are critically assessed in light of the performance of walls from limited available test data. It is concluded that additional test data are needed to justify the use of nonlinear analysis techniques to qualify block walls in nuclear power plants.