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 Behavior of Precast Buildings With Dissipative Connections

Recent earthquakes in southern Europe highlighted that the connections of cladding panels to R.C. frames in precast buildings had a major role in the structural collapse. For this reason, there is an urgent need for a review of the design methods for these connections as well as for an improvement in the manufacturing technology. This article aimed to assess the efficiency of dissipative panel-to-structure and roof connections in R.C. precast buildings. A parametric study consisting of linear and non-linear analyses on one case-study building is performed. Different sensitivity analyses are performed varying their mechanical properties (i.e., stiffness, strength, and ductility) to analyze the behavior of the CP/frame connections. The study focuses on dissipative connections with an elastic–plastic behavior, placed between cladding panels (CPs) and frames in precast buildings with stacked horizontal cladding panels. The introduction of dissipative CP/frame connections implies the inclusion of panels in the global seismic resisting system. The “panels + frame” system highlights a high stiffness until the yield strength of the CP/frame connections is reached. The results, obtained from non-linear dynamic analyses (NLDAs), clearly show how the proposed connection improves the structural seismic performance. By contrast, this is no longer true for R.C. precast structures with flexible diaphragms, especially for intermediate columns, far from panels aligned to seismic action. In this case, significant and unexpected axial forces arise on out-of-plane connections between panels and columns. The integration of an efficient diaphragm is essential to prevent these critical issues both on intermediate columns and CP/column connections; it enables the dissipative capacity of the “panels + frame” system, and it significantly limits the forces and displacements of intermediate alignments. Unfortunately, the achievement of a rigid diaphragm is not always feasible in precast buildings. A possible alternative to activate dissipative capacities of the roof diaphragm with limited in-plane stiffness is the use of dissipative connections linking roof beams and main beams. The solutions described in this article can be applied both in the design of new buildings and for the seismic upgrading of existing ones with easy-to-install and low-impact applications.

Earthquakes Induced by Wastewater Disposal near Musreau Lake, Alberta, 2018–2020

Although hydraulic fracturing-induced earthquakes have been widely reported in Alberta, Canada, only one seismic cluster (the Cordel Field) has thus far been linked to wastewater disposal (WD). In this study, we report a statistically significant spatiotemporal correlation between recent earthquakes and nearby WD wells near Musreau Lake—the second disposal-induced earthquake swarm in Alberta. This newly occurred swarm contains five events with local magnitudes ML>3 from January 2018 to March 2020, forming into three tightly spaced clusters. The refined locations and focal mechanisms suggest a ∼10 km long northwest–southeast-trending rupture along the northern Rocky Mountains that developed over time, during which both poroelastic effects and static stress transfer played key roles. Through a statistical analysis of all reported induced earthquake clusters in the western Canada sedimentary basin (WCSB), we propose a linear predictive relationship (i.e., the “Interpolated Strike Orientation” model) between fault rupture direction and fault distance to the Rocky Mountains. This observation-based model, which is supported by both the focal mechanisms of the natural earthquakes and the nearby northwest-striking geological faults, is a new and useful reference for future assessments of seismic hazard in the WCSB.

Seismic Response Control of Elevated Water Tank using Base Isolation: A Review

Earthquake events are not something which can be avoidable. The Indian subcontinent has a background marked by devasting quakes. Quakes are generally caused when the stone underground out of nowhere breaks along an issue. Ground shake is caused by seismic waves due to sudden release of energy. The Centre of earthquake vibration is known as epicentre. Due to earthquake millions of lives are lost which can never be affordable. Most of the structures are subjected to vibrations; it causes destruction of country’s infrastructure. In the recent earthquakes many well designed concrete structures have been severely damaged or collapsed. To protect structures from response reduction of structures and important harm under such serious earthquakes has become a vital theme in structural engineering. In this investigation, we evaluated seismic performance of staging system of elevated water storage tank with or without Base Isolation by using SAP2000. From this examination the powers following up on elevated water tank because of seismic powers are determined for zone IV.

Out-of-Plane Experimental Study of Strengthening Slender Non-Structural Masonry Walls

Non-structural masonry partition walls, which are mainly designed to functionally separate spaces in the buildings and provide physical barriers between rooms, were traditionally built from either solid or hollow clay units or autoclaved aerated concrete blocks. Recent earthquakes have revealed the high vulnerability of these elements, even in the case of low to moderate seismic events. Public buildings (e.g., hospitals and schools) are particularly vulnerable. Due to their greater floor-to-floor heights and the response spectra of floors, the dynamic response of primary structure may provoke significantly higher seismic loads on partition walls. The main goal of the presented experimental study was to investigate the behavior of slender partition walls loaded out-of-plane with a simple and cost-effective approach that may be applied through routine refurbishment works. Eleven full-scale slender non-structural masonry partition walls were built with brickwork and cement–lime mortar. Eight of them were additionally strengthened with different techniques, including glass fiber-reinforcing fabric and low-cost glass fiber-rendering mesh. To evaluate the efficiency of the applied strengthening solutions, out-of-plane quasi-static cyclic experiments were conducted. By applying meshes over the entire surfaces, the resistance was significantly improved with the low-cost approach reaching half of the resistance of the commercially available strengthening system preserving the same displacement capacity.

Behavioural Study of Infill’s Walls on Soft Story Building

Open ground storey or soft storey is a typical feature in multistory structures in urban areas. This open storey is provided to accommodate parking, reception lobbies, office, communication hall etc. Many of structure having soft storey suffered major damage and collapsed in recent earthquakes. During an earthquake, because of variation in stiffness in soft story and its adjacent floors the inter story drift can occur and the lateral forces cannot be well distributed along the height of building. Lateral forces concentrate on soft story causes large displacement. In this work, an attempt has been made to observe the behavior of gradual decrease in stiffness of building, by using different types of infill material. This work discusses Optimum Earthquake response of tall buildings by response spectrum method as per IS 1893:2002 (Part- I) in ETAB’S software. Seismic parameters like storey stiffness and storey displacement are checked out.

Analysis of Seismic Retrofitting in Heritage Buildings: Techniques and Conservation Interventions

Earthquakes result in major structural damage or outright collapse of buildings. Recent earthquakes have shown that historic buildings retrofitted to withstand earthquakes survive better than those that have not been upgraded. India is a country with a rich architectural and cultural heritage with a large number of religious and secular buildings dating back to the 2nd century BC. Heritage buildings are especially vulnerable in case of an earthquake. If once they are lost a part of our history is lost forever. Although heritage buildings can be retrofitted to survive earthquakes, many retrofit practices damage or destroy the very features that make such buildings significant. So there is a need to conserve these buildings following the International Venice Charter issued in 1966 to regulate the conservation and restoration of monuments and sites worldwide. This paper studies the various aspects of seismic retrofitting of heritage buildings, new techniques being evolved worldwide, and also discusses preservation issues and scenarios of heritage conservation in India.

The 6 May 1947 Milwaukee, Wisconsin, Earthquake

The State of Wisconsin is not known for earthquake activity. The authoritative public-facing U.S. Geological Survey Comprehensive Catalog of earthquakes includes only three small (magnitude < 2) earthquakes in the state, all instrumentally recorded. Although other catalogs include more events in Wisconsin, experience has shown that many types of events, such as explosions and cryoseisms, have made their way into earthquake catalogs in this region. In this short report, I summarize available information about an earthquake that was felt in eastern Wisconsin at 15:27 local time on 6 May 1947. As what appears to be the largest historical earthquake in the State of Wisconsin, it is of public interest, its modest size notwithstanding. It appears that no useful instrumental records exist, due in part to a teleseismic event that occurred approximately 3 min later, generating surface waves that were recorded on early long-period instruments in the region. Instrumental data may exist for this event but have not been found. Comparing the felt area with information from recent earthquakes in the region, I estimate an intensity magnitude of 3.8 for the event, with a subjectively estimated uncertainty range 3.5–4.1. Relatively strong effects, including reports of broken dishes in Milwaukee, and shaking described as short but especially sharp, suggest that the event may have been among the sprinkling of shallow earthquakes now known to occur in the upper Great Lakes region.

Study of Seismic Performance of Chinese-Style Single-Layer Suspended Ceiling System by Shaking Table Tests

During some recent earthquakes, the suspended ceiling system (SCS) in buildings suffered severe damage. The seismic performance of SCS attracted more attention from researchers. In this study, full-scale shaking table tests on two Chinese-style single-layer SCSs with different boundary conditions are conducted. The seismic damage and earthquake responses, including acceleration, displacement, and strain responses, are compared. The effect of the boundary condition on the seismic performance of the SCS is studied. It is found that the seismic performance of the SCS is significantly affected by the boundary condition. Compared with the SCS with the free condition at the boundary, the damage to the SCS installed with seismic clips at the boundary is much slighter. Compared with the SCS with the free condition, the median of acceleration amplification factor (AAF), the peak displacement (PD), and maximum strain of the SCS installed with seismic clips are reduced by up to 63%, 99%, and 84%, respectively. At the end of the tests, the SCS with the free condition at the boundary completely collapsed with 68% of the panels falling, while only 15% of panels fell in the SCS installed with seismic clips. The seismic clips could avoid the falling of the grids from the peripheral support and ensure the integrity of the SCS. With the help of seismic clips installed at the boundary, the responses of the ceiling, such as acceleration, displacement, and strain, decrease significantly, and thereof, the collapse resistance capacity is improved.