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.

Comparative nonlinear seismic analysis of an existing RC bridge designed with obsolete codes

The evolution of seismic design and calculation criteria for highway bridges has a direct influence on their structural behavior. This paper presents a nonlinear dynamic analysis using a detailed 3D finite element model of an existing bridge, with different design criteria for the column transverse reinforcement, according to code requirements of different times. The numerical model is able to simulate both the collapse of the structure and the generation of damage in its elements when subjected to extreme seismic actions. Through the numerical model, it is possible to represent the cyclic behavior of the concrete, and to evaluate the influence of the transverse reinforcement assigned to the column on the overall response of the bridge. The formation of plastic hinges is verified, as well as the identification of different collapse mechanisms.

Method of multiscale coincidence of pulses for measuring temporary loads from moving vehicles in bridges and overpasses

Modern development of road transport is characterized by constant updating of the nomenclature of cars (including heavy-duty vehicles), by increasing of intensity and speed of their movement, especially in large metropolises and on roads of national and local significance. This complicates the operating conditions of spans of highway bridges to some extent, leads to their damage and early wear. The deterioration of the technical condition of the structures of the spans is largely due to the increased dynamic impact of the cars on the bridges. The purpose of this article is to measure the amplitude of oscillations of a bridge structure from temporary loads of rolling stock with non-periodic long-term loading by optical methods. In accordance with this goal, it is necessary to develop a technique and device for measuring the amplitude of oscillations of the bridge structure by converting the amplitude of oscillations in time intervals and their subsequent measurement by multi-scale pulse coincidence. In a number of works, digital deployment systems that use number systems with different bases, represented by a family of deployment functions, are considered in detail. Such digital systems in general, are described by the corresponding operating scheme. According to this operating scheme, a method of multiscale matching for measuring time intervals was developed, which formed the basis for measuring the vibration amplitude of the bridge structure. The given mathematical model of calculation of the number of measurement channels was used in the synthesis of velocity transducers and linear displacements based on optical (laser) deployment systems, information conversion devices of radar velocity sensors based on the Doppler effect. Similarly, a frequency comparison device, a digital frequency meter, a digital phase meter, and a number of other frequency-time group devices were synthesized.

Finite Element Analysis and Long-Term Monitoring of a Highway Overpass Bridge with Newly Constructed Link Slabs and Modified Bearings

Joint failure, which causes leakage in bridge decks as well as deterioration in girders and substructures, is one of the most common concerns in highway bridges. Therefore, link slabs have been considered as a preventive maintenance method in eliminating these joints. This paper presents a pilot project that constructed the link slab system in Maryland, U.S., with modified bearings to improve its durability and reduce maintenance costs. Compared with the traditional bearing replacement design for the link slab systems, this project proposes a more economical method by removing the anchor bolts and restricting sliding plates of the fixed bearings at both abutments to match the designed boundary conditions while avoiding the high cost of jacking girders and replacing bearings. Furthermore, numerical analysis and structural health monitoring were conducted and validated to investigate the effectiveness of the link slab design with various high performance concrete materials. After the one-year monitoring period, the link slab system is verified to be in fully functional condition and the bearing modification design is verified to be effective.

Unexpected soil amplification effect on seismic performance of highway bridges during the Aegean earthquake of October 2020, Mw 6.6

On October 30, 2020, an earthquake about 70 km away from the city center of Izmir with a 4.3 million population has shaken the city tremendously and has resulted in destruction of many building type of structures due to an unexpected high soil-amplified vibrations very similar to the Mexico City earthquake in 1985. The bridges at the soil-amplified sites has performed in elastic range with no damage at all. In the city of Izmir, the 42 year old twin bridges located on the main transportation route, were tremendously shaken by the earthquake had observed to have no seismic induced damage. Surprisingly twin bridges suffering from the alkali silica reaction (ASR) over the years did not even pound to each other despite the small size of longitudinal gap between them. As it has been known, the past performance of Turkish designed bridges are typically succesfull with almost no damage as observed in the Van 2011 and Sivrice 2020 earthquake mainly due to allowing movements at their joints and to flexible type of framing. The focus of the paper is given to understand the successful performance of bridges and to investigate the non-pounded twin bridges of the Izmir city. In this scope, a bridge inspection has been performed and the twin bridges have been analyzed for the recorded ground motion. The results have indicated that the structures have been subjected to 0.3 g at their vibration modes and the twin bridges have a synchronized motion due to having the identical vibration mode shape with a period of 1.5 seconds