Bashir Alam

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.

Experimental Seismic Performance Evaluation of Unreinforced Brick Masonry Buildings

This paper presents an experimental study on the performance of a full-scale unreinforced brick masonry (URM) building system tested under quasi-static loading at the Earthquake Engineering Centre, University of Engineering and Technology in Peshawar, Pakistan. The configuration and materials used in the single-story URM building are typical of those found in the northern areas of Pakistan affected by the 2005 Kashmir earthquake. This study is a part of ongoing research for the earthquake impact assessment of the city of Abbottabad. Combined shear and flexural behavior was observed during the test. The experimental data was analyzed and is presented in the form of force-deformation hysteresis loops and envelope curves. Based on the measured data, different performance levels have been established. The measured response of the test structure is also compared to the estimated response obtained using three capacity evaluation procedures and the two are found to be in good agreement.

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.

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.

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.

Seismic Capacity Assessment of Confined Brick Masonry Building: An Experimental Approach

Brick masonry is widely used for building construction throughout the world. However, unreinforced brick masonry buildings performed poorly in the 2005 Kashmir earthquake, in Pakistan, resulting in a decline in the use of brick masonry. In order to investigate and quantify the performance of brick masonry against the seismic forces by confining it through typical stiffer, line elements (column and beams), a full-scaled room model of an area 3048 × 3658 mm (10 × 12 ft) and height of 3353 mm (11 ft) was constructed using confined brick masonry. The model was tested under quasistatic loading system. Crack pattern was noted at the end of each loading cycle. The response of the model was interpreted through a hysteresis curve, which was then idealized by a bilinear curve. A comparison of the results has been made with four different studies done on the similar model made of unreinforced brick masonry before and after retrofitting and unreinforced concrete block masonry before and after retrofitting previously tested at the same testing facility.

Effects of pounding on adjacent buildings of varying heights during earthquake in Pakistan

Abstract Pounding occurs when the adjacent buildings start vibration out of phase during the seismic activity which causes collision amongst the adjacent buildings. There are many mitigation techniques to avoid or minimize the effects of pounding including the provision of minimum separation gap between the adjacent buildings. Although all codes have provided the minimum separation gap requirements for the buildings, still a lot of study is required on this topic. This research aims at finding the minimum gap requirement for midrise buildings in Pakistan. Adjacent Buildings with different geometry and height are modelled in Sap2000 software with varying gap elements. Pushover and In-elastic time history analysis of these buildings are carried out using ground motion of Kashmir earthquake. Buildings are assumed to be resting on stiff soil. Material and sectional properties are also remained same for all cases. In order to reduce the pounding effects of two buildings, they were attached with each other and top displacements of buildings were compared with separate buildings with inadequate gap. Column shear, maximum peak displacements and square root of sum of squares of maximum peak displacements were studied and the results were plotted graphically. It was found out that pounding can occur up to separation gap of six inch. Maximum pounding occurs at the top floor level of smaller building. The requirement for minimum gap in UBC 97 is found out to be conservative.

STABILITY ANALYSIS OF SOIL SLOPE IN SWABI, PAKISTAN

In this study, slope stability analysis for a particular type of soil in Swabi area was carried out using the method of slices. Gravity load and seismic load were considered in the stability analysis. SLOPE/W and SIGMA/W software of Geo studio package were used for analysis under both dry and completely saturated conditions. Pseudo-static approach was used for the seismic stability analysis. The peak ground acceleration value for stability analysis was obtained from the seismic hazard analysis. Two soil slope conditions were considered, and one was found in critical condition. Retaining wall, Soil nails and ground anchors were assumed in the analysis for stability of slope with critical condition. Peak ground acceleration value of 0.235g is determined with site specific deterministic seismic hazard assessment approach. The maximum displacement in the soil slopes with retaining wall, soil nails, and ground anchors are 0.0220, 0.01665 and 0.01529 feet respectively. Results showed that using ground anchors have a factor of safety 1.165 and both the horizontal and vertical deformation values are within the limit. Based on results, ground anchors technique was found to be a suitable method for slope stability in Swabi.

MOISTURE DAMAGE IN ASPHALT MIXTURES FROM SATS TEST AND X-RAY CT

This study investigated damage in asphalt due to moisture by using the modified SATS (saturation aging tensile stiffness) test along with image analysis. Specimens made from granite aggregate and limestone aggregate and of high grade (hard) bitumen were tested in the modified SATS test. The samples were scanned within an X-ray CT before the testing using SATS, after the initial saturation and at the completion of SATS test. Bitumen was extracted from tested specimens and scanned separately in a high resolution Nanotom. The extracted bitumen was tested in a DSR for Shear properties. The specimens made from granite (acidic) and limestone (basic) aggregate were found to have similar permeability and was high for specimens having high design void content. Specimens made from basic aggregate had higher stiffness value than the specimens made from acidic aggregate. The Master curve of aged binder is different to that of virgin binder (bitumen). The microstructure of binder observed was different for aged and virgin binder.