SEISMIC VULNERABILITY OF REINFORCED CONCRETE BRIDGES IN PAKISTAN

Different researchers have performed seismic hazard assessment studies for Pakistan using faults sources which differ from Building Code of Pakistan (BCP 2007) with diverse standard deviations. The results of seismic hazard studies indicate that BCP requires gross revision considering micro and macro level investigations. The recent earthquakes in Pakistan also damaged bridge structures and some studies have been conducted by different researchers to investigate capacity of existing bridges. The most of bridge stock in Pakistan has been designed assuming seismic loads as 2%, 4% and 6% of dead loads following West Pakistan Code of Practice for Highway Bridges. The capacity of eight selected real bridges, two from each seismic zone 2A, 2B, 3 & 4 is checked against BCP demands. Static and dynamic analyses were performed and the piers were checked for elastic limits. It is established that piers are on lower side in capacity and the bridges in zone 2A are generally less vulnerable. Whereas the bridges in zone 2B, 3 and 4 are vulnerable from medium to very high level. Hence, an in-depth analytical vulnerability study of bridge stock particularly in high-risk zone needs to be conducted on priority and appropriate seismic retrofitting schemes need to be proposed.

Seismic Strengthening of RC Structures Using Wall-Type Kagome Damping System

In this study, the Kagome truss damper, a metallic wire structures, was introduced and its mechanical properties were investigated through theoretical analyses and experimental tests. The yield strength of the Kagome damper is dependent on the geometric shape and diameter of the metallic wire. The Kagome damper has higher resistance to plastic buckling as well as lower anisotropy. Cyclic shear loading tests were conducted to investigate the energy dissipation capacity and stiffness/strength degradation by repeated loadings. The hysteretic properties obtained from the tests suggest that a modification of the ideal truss model with a hinged connection could be used to predict the yield strength and stiffness of the damper. For seismic retrofitting of a low-rise RC moment frame system, a wall-type Kagome damping system (WKDS) was proposed. The effectiveness of the proposed system was verified by conducting cyclic loading tests using a RC frame with/without the WKDS (story drift ratio limit 1.0%). The test results indicated that both the strength and stiffness of the RC frame increased to the target level and that its energy dissipation capacity was significantly enhanced. Nonlinear static and dynamic analyses were carried out to validate that the existing building structure can be effectively retrofitted using the proposed WKDS.

Numerical investigation of ground tanks for storage subjected near-fault earthquakes

Finite element method is known as the most common methods in a numerical analysis of reservoirs subjected to the influence of an earthquake. Investigating the effects of interaction between structures and fluid during the earthquake is among the major objectives of the present research. In this article, by selecting a variety of conventional modes of fluid storage, the dynamic effects of the reservoir and their mutual effects based on changes in physical parameters are analyzed. Unexpectedly, based on the results of this study, it was observed that the crisis situation always does not occur in the full state of the tank. Moreover, the filled and semi-filled reservoirs require seismic retrofitting for mode 10% below the tank height.

Optimizing Seismic Capacity of Existing Masonry Buildings by Retrofitting Timber Floors: Wood-Based Solutions as a Dissipative Alternative to Rigid Concrete Diaphragms

The inadequate seismic performance of existing masonry buildings is often linked to the excessively low in-plane stiffness of timber diaphragms and the poor quality of their connections to the walls. However, relevant past studies and seismic events have also shown that rigid diaphragms could be detrimental for existing buildings and do not necessarily lead to an increase in their seismic performance. Therefore, this work explores the opportunity of optimizing the retrofitting of existing timber floors by means of a dissipative strengthening option, consisting of a plywood panel overlay. On the basis of past experimental tests and previously formulated analytical and numerical models for simulating the in-plane response of these retrofitted diaphragms, in this work nonlinear incremental dynamic analyses were performed on three case–study buildings. For each structure three configurations were analyzed: an as-built one, one having floors retrofitted with concrete slabs and one having dissipative diaphragms strengthened with plywood panels. The results showed that the additional beneficial hysteretic energy dissipation of the optimized diaphragms is relevant and can largely increase the seismic performance of the analyzed buildings, while rigid floors only localize the dissipation in the walls. These outcomes can contribute to an efficient seismic retrofitting of existing masonry buildings, demonstrating once more the great potential of wood-based techniques in comparison to the use of reinforced concrete for creating rigid diaphragms.