Akhtar Naeem Khan

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.

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.

Neural Network Based Attenuation of Strong Motion Peaks in Europe

Artificial Neural Network (ANN) is used in this article to develop attenuation relationships for three peak ground motion parameters, namely, peak ground acceleration (PGA), peak ground velocity (PGV), and peak ground displacement (PGD). This article demonstrates the capability of ANN to capture the key physical aspects of seismic wave attenuation and region specific earthquake characteristics. Limited strong ground motion data and no particular functional form except for few constraints are used in the development of ANN based attenuation relationships. The database consists of 358 records (2 horizontal components of ground acceleration at each station) from 42 European shallow earthquakes. The surface magnitude (Ms), distance of site from surface projection of the rupture (R), and broad categories of soil type (soft soil, stiff soil, and rock formation) are the three input parameters. The Ms ranges from 5.5–7.9 and R ranges from 3 – 260 Km. The model is trained using 75% (134 data points) of the total data, while the remaining 25% (45 data points) of the total data is used to test the performance of the trained neural network models. The ANN is able to derive attenuation relationships which are consistent with the theory of ground motion attenuation phenomena. ANN can, therefore, be used as an alternative method to conventional regression techniques for developing attenuation relations, particularly for regions where limited earthquake data is available.

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.

A Survey of Damages to Bridges in Pakistan after the Major Earthquake of 8 October 2005

An earthquake measuring Mw 7.6 struck the Pakistan-administered part of Kashmir on 8 October 2005. The epicenter of the earthquake was located 22 km from the city of Muzaffarabad. The earthquake resulted in the loss of more than 80,000 lives and caused extensive damage to property and infrastructure. A survey of an approximately 400-km road network was carried out, in which 90 bridges were inspected for earthquake-associated damage, out of which 14 bridges (16%) experienced damage of varying degrees, of which nine bridges (10%) either failed or became nonfunctional. The survey revealed some of the deficiencies of the construction practices in Pakistan and also highlighted the need for improvement to the countrys current bridge design practices. This paper reports the prominent types of failures observed and discusses the deficiencies in current design practices. Based on the findings of the survey, various recommendations are made, with the objective of minimizing earthquake-associated damages to new and existing bridges in areas with a high seismic risk.

Experimental Behavior of Full Scale URM Building Retrofitted with Ferrocement Overlay

This paper presents a study on the behavior of a damaged full scale unreinforced brick masonry building, retrofitted with ferrocement overlay and cement based grout injection, tested under cyclic loading. Damage mechanism and force-deformation behavior of the retrofitted structure are compared with its pre-damaged response to quantify the beneficial effects of retrofitting scheme. The lateral load capacity of the retrofitted building was significantly improved and the damage mechanism was transformed from mixed compression-flexural-shear mode to a more stable flexural rocking mode. The energy dissipation capacity, however, remained unchanged and the deformation capacity was slightly decreased.

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.

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.