Qaisar Ali

Observed Seismic Behavior of Buildings in Northern Pakistan During the 2005 Kashmir Earthquake

Recent earthquakes in Pakistan demonstrated that the region is highly seismic. Masonry buildings constructed with stones, concrete blocks, and fired-clay bricks and concrete buildings were damaged during the 8 October 2005 Kashmir earthquake. This paper presents the seismic behavior of reinforced concrete and masonry buildings in northern part of the North-West Frontier Province (NWFP) and Kashmir during the earthquake. Most of the buildings were observed to be nonengineered or semi-engineered. The paper presents an overview of the 1937 Quetta building code and the 1986 and 2007 building codes of Pakistan. Lessons learned during the earthquake are also presented.

In-Plane Behavior of the Dhajji-Dewari Structural System (Wooden Braced Frame with Masonry Infill)

This paper presents experimental and numerical investigations conducted on typical dhajji buildings found in the northern mountainous areas of Kashmir and surrounding regions to evaluate their in-plane lateral load response. The experimental work included an in-plane quasistatic cyclic test on three full-scale walls as well as monotonic tension and bend tests on main connections. The test results show that the dhajji-dewari system of buildings possesses tremendous resilience against lateral forces. The function of connections, especially the connections between the vertical posts and bottom plate, control the performance of the system. The test results also indicate that although masonry infill does not contribute to lateral load capacity, it significantly increases the energy dissipation capacity of system. The data accrued from the tests has been used in nonlinear static push-over analysis of the numerical models to develop simplified analytical tools for facilitating lateral load performance evaluation of dhajji structures.

Seismic Behavior of Unreinforced and Confined Brick Masonry Walls Before and After Ferrocement Overlay Retrofitting

This study presents experimental results of quasi-static load test conducted on two full-scale brick masonry walls, one unreinforced and the other confined, to investigate their in-plane lateral load behavior before and after retrofitting. The walls were constructed closely following the masonry system commonly used in Pakistan and in most South Asian countries. The walls before retrofitting were tested to their peak resistance. The damaged walls were then retrofitted with grout injection followed by ferrocement overlay and retested to their ultimate failure under the identical conditions. The effectiveness of the proposed confinement and retrofitting scheme was assessed from the damage pattern, energy dissipation, and force-deformation behavior of the walls tested before and after retrofitting. The test results before retrofitting show that the capacity of confined masonry wall is almost double to that of unreinforced masonry wall. The test results after retrofitting indicate that the applied retrofitting scheme significantly enhanced the lateral load capacity of the unreinforced masonry wall, however it was marginally beneficial in the confined masonry walls. The test results are also compared with American Society of Civil Engineers (ASCE) standards in terms of stiffness, strength and acceptable deformations. It is concluded that the guidelines provide reasonable estimates of the test observations.

Displacement-Based Earthquake Loss Assessment of Masonry Buildings in Mansehra City, Pakistan

A simplified nonlinear displacement-based approach is presented herein for earthquake loss estimation of structures. The methodology compares the displacement capacity of the structural systems with the displacement demand at the characteristic vibration periods of the systems taking into account their energy dissipation and the inherent variability in the seismic demand besides the variability in the geometric and material properties of the structural systems. To calibrate the methodology for Pakistani urban masonry buildings, 3D nonlinear dynamic time-history analysis of masonry buildings is performed, using a simplified formulation proposed herein, in order to obtain their vibration periods. Further calibration of the method is performed by analyzing experimental data on masonry shear walls. Deformation limit states of the masonry shear walls at different performance levels are presented. The energy dissipation characteristics of the masonry shear walls are quantified and presented in a simplified analytical form. A case study application is performed for the estimation of direct socio-economic losses in the urban area of Mansehra City for scenario earthquakes.

Seismic Resistance Evaluation of Unreinforced Masonry Buildings

The article presents seismic resistance evaluation study of unreinforced brick masonry buildings. The study was carried out as part of the Ph.D. research work of the first author. As part of the study, in addition to the standard laboratory tests, a dynamic field test was carried out on single-story, single-room unreinforced masonry structure. The model structure was tested in actual ground conditions against simulated earthquake vibrations produced through controlled explosions, especially designed for this purpose. Based on masonry properties accrued from lab and field tests, finite element models of the brickwork system were also studied. Finally, the software named, “Shear Damage Index (SDI),” developed as part of this study, was used to plot contours of shear demand (shear stress) to shear capacity (shear strength) ratio on the numerical model and hence to identify potential weak zones in the model for possible strengthening of those locations.

Seismic Performance of Stone Masonry Buildings Used in the Himalayan Belt

Rubble-stone masonry structures are found abundantly in the Asian countries along the Himalayan range. Such structures are usually constructed in dry-stone masonry or are constructed in mud mortar, which makes them susceptible to damage and collapse in earthquakes. In order to study the seismic behavior of these structures, dynamic shake table tests on three reduced-scale rubble-stone masonry models were conducted. The models comprised a representative school building, a residential building, and a model incorporating simple cost-effective features in the form of horizontal and vertical reinforced concrete elements. This paper presents the results of shake table tests carried out on rubble-stone masonry buildings including: damage pattern, capacity curves, damage limit states, and response modification factors of these structures. Test data indicates that seismic performance of rubble-stone masonry structures can be significantly improved by incorporating cost-effective features such as vertical members and relatively thin horizontal bands.

Performance of Pakistani volcanic ashes in mortars and concrete

Two Pakistani volcanic ashes, VA1 (as is and calcined) and VA2 (as is), were incorporated into mortar cubes, concrete cylinders, and concrete beams as a partial substitute for ordinary Portland cement (OPC), and were studied in detail. The X-ray diffraction patterns showed that both ashes possessed crystalline as well as amorphous phases. The pozzolanic activity index (PAI) of VA1 at 7 d was below 75%, whereas it was 80% at 28 d. The pozzolonic activity indices in OPC mortars containing VA2 were much higher than those for VA1, both at 7 and 28 d. In mortar cubes and concrete cylinders, approximately the same compressive strengths were observed in samples containing 100% cement as in those incorporating a 10% replacement of cement by either VA1 or VA2. Mortar cubes soaked in 5% sodium sulphate solution demonstrated consistently improved resistances to sulphate attack as ash content increased in the mortar. Similar results were also observed in water absorption tests. Modulus of rupture of all concrete beam...

Experimental Seismic Performance Evaluation of Unreinforced Brick Masonry Shear Walls

Unreinforced masonry buildings, constructed with stones or bricks, are common in the northern areas of Pakistan. In the October 2005 Kashmir earthquake, the seismic performance of stone masonry buildings was found to be poor, which was the primary source of fatalities. Unreinforced brick masonry (URBM) buildings, however, performed well even in severely jolted areas. The performance of URBM could have been much better if the affected buildings were constructed by using proper guidelines. Taking lessons from the disaster, an experimental investigation, based on typical geometry and precompression levels of the URBM shear walls in the affected region, was conducted to evaluate their seismic performance. Twelve walls were tested in the in-plane direction using quasi-static cyclic loading. First-story drift ratios for various performance levels in URBM buildings are proposed. The influences of relative precompression level and aspect ratio on the damage pattern, ultimate drift ratio, and equivalent viscous damping of the walls are examined.

A Proposal for a Comprehensive Approach to Safer Non-engineered Houses

Abstract Reducing earthquake disasters in non-engineered houses is an acute issue because they are a main cause of human casualties worldwide. Since non-engineered houses differ from engineered houses in many respects, the authors conducted a comparative study and clarified the characteristics of the former. Based on this study, they found that reducing disasters in non-engineered houses would require appropriate seismic technologies to be adopted by communities and effective channels to disseminate technical knowledge. Further, a comprehensive approach covering a wider field of activity and effort was found to be necessary as users/dwellers of non-engineered houses are low/middle-income people and a professional housing supply sector usually does not exist for such houses. This paper reports on the characteristics of non-engineered houses, indicates the items to be tackled in reducing earthquake disasters in such dwellings, and proposes an approach to safer non-engineered houses consisting of key issues and a comprehensive approach.

Seismic Performance Assessment of Non-Compliant SMRF-Reinforced Concrete Frame: Shake-Table Test Study

ABSTRACT Seismic performance assessment is carried out for reinforced concrete structure built in low-strength concrete lacking confining ties in beam-column joint. Shake-table tests were performed on 1/3rd scaled two-story frame using design-spectrum-compatible accelerogram, scaled to various target levels. The frame is observed with beam longitudinal bar slip and pullout. Joints with no confining ties experienced extensive damage, observed with cover/core concrete spalling. The frame could resist 70% of the design ground motion to remain within the code-specified drift limit. The code requirement for minimum column depth will not avoid joint damageability in case of low-strength concrete and joints lacking confining ties.