Many bridges built in the past 50 years are reinforced Concrete. Because of their normal deterioration, the introduction of new safety standards, and the increasing traffic volume and loads, a high percentage of the older bridges require rehabilitation or expansion. Often, the choice between constructing a new bridge and rehabilitating the existing one must be made. An essential factor in making a sound decision is knowledge of the strength of the bridge in its existing form. Unfortunately, the inelastic response, load distribution characteristics, and ultimate strength of bridges can not be realistically assessed by use of simplified procedures currently used for design and evaluation. Prediction of this behavior ultimately requires extensive experimental tests or advanced analytical techniques. In many cases, analytical methods are more economical and expedient than laboratory or field testing, and a number of researchers have extolled the potential of using finite element analysis to predict bridge response.The primary objective of this study is to establish and demonstrate a convenient, reliable, and accurate methodology for analyzing reinforced Concrete structures with particular emphasis on Reinforced Concrete Bridge and develop a capability for predicting stress and strain distribution through the thickness of bridge decks. A secondary objective of the analytical evaluation include the development of a finite element model that could correctly represent global bridge behavior and accUl1telypredict strains, stresses and displacements in the deck. A specific objective is to investigate the enhancing effects of compressive membrane action on the ultimate flexural strength of bridges.A nonlinear finite element program, NONLACS2, developed by Kheyroddin, was selected as the basic platform for this study. The next step was to demonstrate how reinforced Concrete is modeled within NONLACS2 and to validate the results predicted by the NONLACS2 program by comparing them with relevant experimental data and accepted design calculations. The finite element model of a reinforced Concrete beam, simply supported, and subjected to a uniformly distributed load, was initially investigated. Further verification of the validity of finite element models of reinforced Concrete components were demonstrated by comparing the predicted response of the model with experimental results obtained from laboratory tests of a two-way reinforced, simply supported, Concrete slab. Tests on existing slab and beam bridges around the world have shown that many of these structures possess a greater load capacity than current design codes predict they should have. Many researchers attribute the additional capacity to a phenomenon known as compressive membrane action. Compressive membrane action occurs as a result of in plane restraints that restrict the horizontal expansion of the bridge deck as it deflects vertically. For this purpose, finite element modeling of slabs with idealized end restraints has been carried out.With the information acquired through the research proposed in this paper, a more complete understanding of the nonlinear behavior of RC bridges was obtained. This would allow a more realistic assessment of the flexural strength of these bridge types to be made. Some important points can be noted. The type of end restraint imposed on a slab significantly affects its load deflection behavior. The ultimate load capacity of a slab with fully restrained ends is almost five times greater than that of a simply supported slab. The stiffness of the horizontally restrained slabs is also significantly greater. The behavior of slabs with pinned ends depends greatly on the height at which the horizontal support acts. T-shape beam have a high lateral strength rather than rectangular beam and cause decreasing of deflection of deck. The stiffness of the T-shaped beams was largely responsible for the mode of failure.

Long-term seismic performance determination of reinforced Concrete bridges is one of the effective factors in service life estimation of these structures. Chloride induced corrosion results in deterioration of critical members in the service life of reinforced Concrete bridges and therefore leads to degradation of long-term seismic performance of the bridge. Due to seismicity and high rate of corrosion in reinforced Concrete structures due to the corrosive environmental condition in Persian Gulf region, evaluation of corrosion-induced degradation on the long-term seismic performance of existing bridges in this region has a high importance. In order to evaluate this problem, at first based on studies done related to Persian Gulf region, corrosion initiation time of columns as critical seismic members of the bridge has been determined. Then effects of corrosion on the reinforced Concrete column at specific time intervals (0, 15, 30, 45, 60, 75, 90 years) in bridge service life have been calculated. Effects of corrosion include degradation of cover and core Concrete, steel, and bonding between Concrete and steel that result in modification of stress-strain relationship of materials. In the next step, at each time interval based on the modified stress-strain relationship of materials, moment-curvature analysis of bridge column conducted and characteristics of plastic hinge have been determined. Finally, based on plastic hinge characteristic at each time interval, pushover analysis of bridge in longitudinal and transverse directions conducted and bridge capacity curves at mentioned time intervals have been compared. Results indicate the time-dependent degradation of bridge capacity under corrosion. According to the obtained results, in order to ensure the long-term seismic performance of reinforced Concrete bridges in corrosive environments, value for an increase of design base shear has been proposed.

The seismic behavior of Concrete end diaphragms of bridges has not been studied before and there are no significant design provisions available. According to the American Association of State Highway and Transportation Officials (AASHTO), the end diaphragms being part of the seismic load path have to remain elastic under the prescribed seismic design forces, regardless of the type of bearings used. In this paper, using a three dimensional finite element model and nonlinear time history analyses, the behavior of reinforced Concrete end diaphragms in straight single-span slab-girder bridges has been investigated. The results are compared to AASHTO's design provisions. It is concluded that for slab-girder Concrete bridges, the Concrete diaphragms remain elastic under design earthquake loading. It is also concluded that AASHTO's recommended seismic design force for end diaphragms could be unsafe in most cases.

The seismic vulnerability of highway bridges remains an important problem and has received increased attention as a consequence of unprecedented damage observed during several major earthquakes. A significant number of research studies have examined the performance of skew bridges under service and seismic loads. The results of these studies are particularly sensitive to modeling assumptions in view of the interacting parameters. In the present study, three-dimensional improved beam-stick models of two-span highway bridges with skew angles varying from 0o to 60o are developed to investigate the seismic response characteristics of skew box girder bridges.The relative accuracy of beam-stick models is verified against counterpart finite element models. The effect of various parameters and conditions on the overall seismic response was examined such as skew angle, ground motion intensity, soil condition, abutment support conditions, bridge aspect ratio, and foundation-base conditions.The study shows that the improved beam-stick models can be used to conduct accurate nonlinear time history analysis of skew bridges. Skew angle and interacting parameters were found to have significant effect on the behavior of skewed highway bridges. Furthermore, the performance of shear keys may have a predominant effect on the overall seismic response of the skew bridges.

bridges are divided into three categories of integral, semi-integral, and conventional (seat type) bridges, based on the connection of deck to abutment. The integral and semi-integral bridges have been widely used recently, while the interactions of soil with abutments and piles are important issue in designing them. However, limited studies have been carried out on the behaviors of integral and semi-integral bridges and, hence, a few specific and suitable designing indices for them can be found. In this study, a 3D finite element model for each type of bridges was developed and analyzed under seismic load. Due to the importance of soil-structure interaction, non-linear springs (links) were employed to simulate the effects of soil behind abutments and soil around piles on the structure. This study determined the effects of seismic loading on the abutment and its backfill soil in the conventional, integral and semi-integral bridge models, and also compared the equivalent exerted force from backfill soil to structure in these three types of bridge models.

bridges play a vital role in transportation, traffic management, and providing access to strategic locations, especially during crises. Earthquakes are unpredictable events that disrupt critical transportation routes and damage important structures. Innovative technologies, such as Ultra High-Performance Concrete (UHPC), offer hope for enhancing structural flexibility and reducing damage. UHPC, known for its uniformity, low permeability, and durability, increases the resistance of bridges to seismic forces and limits the spread of damage. One of the most effective methods for assessing seismic vulnerability is Fragility Analysis. This study evaluates urban bridges with UHPC Concrete columns supporting cast-in-place Concrete T-beam superstructures. The analysis was conducted using CSI Bridge software, and appropriate ground motion records were selected for Incremental Dynamic Analysis (IDA) and damage level calculations. The results indicate that the probability of damage exceeding a certain threshold in UHPC Concrete piers is lower compared to those made of ordinary Concrete. Examining damage intensity levels reveals that high-performance Concrete improves performance by 7% in the worst-case scenario and up to 26% in the best-case scenario compared to ordinary Concrete.

Conducting evaluation studies on the bridges used on the road surface is one of the most important time-consuming and costly processes, especially considering the high number of bridges in Iran, i.e., more than 35 thousand in the whole country and 8658 bridges in Zanjan province. On the other hand, the time and cost of these studies can cause delays in carrying out studies for all bridges and cause irreparable damages due to a lack of proper management of bridge repair and maintenance. Taguchi's test design method is one of the methods that predict the desired combination with the help of statistical and mathematical models, by defining its orthogonal arrays, instead of performing all possible evaluation options, by performing a limited number of evaluations. In this research, based on the Taguchi method, instead of examining 8658 bridges with 13 different criteria, only 27 combinations of the physical characteristics of bridges and atmospheric, climatic and traffic conditions affecting Concrete road bridges in 5 main axes of Zanjan province were determined the deterioration indices of bridges with these combinations were calculated.It showed that the combination of bridges with 2-3 times of snow along the axis, 91-100 days of frost during the year, 26-30% of heavy vehicles passing over the bridge and a length of 7.1-12 meters has the highest structure failure index with an estimated average of 76.2725, which will lead to the highest failure risk. This means that this combination has created the highest risk of damage. Also, the most important factor in the failure of bridges is the percentage of passing heavy vehicles compared to the total traffic.

bridges constitute an expensive segment of construction projects; the optimization of their designs will affect their high cost. Segmental precast Concrete bridges are one of the most commonly serviced bridges built for mid and long spans. Genetic algorithm is one of the most widely applied meta-heuristic algorithms due to its ability in optimizing cost. Next to providing cost optimization of these bridge types, the effects of each one of the main three selections, crossover and mutation operators are assessed, and the best operator is determined through the Taguchi experimental design. To validate the functionality of this algorithm, a bridge constructed in the city of Isfahan, Iran (completed in 2017) is optimized, a total of 13% reduction in cost and weight of its superstructure is evident. The efficiency of applying the Taguchi method in determining the type of operators of the genetic algorithm is proved.