Effect of Plastic Hinge Properties in Nonlinear Analysis of Highway Bridges

Current design practice of highway bridges is moving towards an increased emphasis on nonlinear static analysis methods. Modelling for such analysis requires the determination of the nonlinear properties of the bridge elements that are expected to behave nonlinearly. Nonlinear static analysis is carried out for either user-defined nonlinear hinge properties or automated-hinge properties, as available in the software SAP2000. User defined hinge properties can be obtained using the recommendations of the Seismic Retrofit Manual by the Federal Highway Administration. Automated-hinge properties in SAP2000 are computed automatically from the element material and section properties according to Caltrans criteria. The bridge designer needs to be aware of that the majority of old bridges were built with little or no consideration to seismic forces and plastic hinge detailing requirements. Therefore, the use of automated-hinge properties for old bridges in nonlinear static analysis may lead to unrealistic displacement capacities. In this study, pushover analysis of two highway bridges built with little attention to seismic forces was performed in an effort to evaluate the difference in global response predicted by using the user-defined nonlinear hinge properties or automatedhinge properties in the software SAP2000. The results demonstrated that user-defined hinge model is capable of capturing the effect of local failure mechanisms, in the plastic hinge region, on the global response of the bridge; while the automated-hinge model can not capture this effect. Therefore, automated-hinge properties should be used with a lot of care, especially for old bridges that might include local failure mechanisms in the plastic hinge region

Effect of Microsilica and Water Proofer on Resistance of Concrete to Phosphoric Acid Attack

This paper investigates the effect of microsilica (MS), water proofer (WP) and MS-WP contents on the durability of concrete to phosphoric acid attack. Three MS replacement levels and three WP mixes were considered in the study: 10%, 15% and 20% by weight of cement for MS and mixes of 0.4, 0.6 and 0.8 L for WP. The water to cement ratio was considered to be constant. The workability, durability of concrete to freezing thawing after 300 cycles, durability of concrete to phosphoric acid attack after 15 cycles of wetting and drying in phosphoric acid solution, compressive strength and modulus of rupture after 28 days were investigated. The degree of acid attack was evaluated by measuring the loss in weight. The study showed that the combined effect of MS-WP improved the durability of concrete to freezing thawing and to phosphoric acid attack without significantly reducing the compressive strength or modulus of rupture of the concrete. The optimum mix was 10% of MS replacement and 0.8 L of WP

Improving Durability of Concrete to Phosphoric Acid Attack

This paper investigates the effect of microsilica, water proofer and super plasticizer on the durability of concrete to phosphoric acid attack, in addition to their sole and combined effects on workability, air content, modulus of elasticity, durability to freezing thawing, compressive strength and modulus of rupture after 28 days. Different microsilica, water proofer and super plasticizer contents were considered: 10%, 15% and 20% by weight of cement for microsilica, 0.4, 0.6 and 0.8 L for water proofer and 0.15, 0.2 and 0.25 L for super plasticizer. The water to cement ratio was considered to be constant in this study. The degree of acid attack was evaluated by measuring the percentage changes in weight of concrete cubes. The results showed that the combined effect of microsilica and water proofer was the best to enhance the durability of concrete to phosphoric acid attack without major effect on the response of concrete to other factors. The optimum concrete mixes were 10% microsilica with medium portions of water proofer

Impact of Plastic Hinge Properties on Capacity Curve of Reinforced Concrete Bridges

Pushover analysis is becoming recently the most practical tool for nonlinear analysis of regular and irregular highway bridges. The nonlinear behaviour of structural elements in this type of analysis can be modeled through automated-hinge or user-defined hinge models. The nonlinear properties of the user-defined hinge model for existing highway bridges can be determined in accordance with the recommendations of the Seismic Retrofit Manual by the Federal Highway Administration (FHWA-SRM). Finite element software such as the software SAP2000 offers a simpler and easier approach to determine the nonlinear hinge properties through the automated-hinge model which are determined automatically from the member material and cross section properties. However, the uncertainties in using the automated-hinge model in place of user-defined hinge model have never been addressed, especially for existing and widened bridges. In response to this need, pushover analysis was carried out for four old highway bridges, of which two were widened using the same superstructure but with more attention to seismic detailing requirements. The results of the analyses showed noticeable differences in the capacity curves obtained utilizing the user-defined and automated-hinge models. The study recommends that bridge design manuals clearly ask bridge designers to evaluate the deformation capacities of existing bridges and widened bridges using user-defined hinge model that is determined in accordance with the provisions of the FHWA-SRM

Stability Analysis of Composite Panels with Stiffeners and Circular Cutouts

Buckling of simply supported square orthotropic plates with multi-blade stiffeners is addressed herein. An approximate, semi-analytical model for such plates subjected to in-plane loading is derived. The optimal buckling load of simply supported laminated composite blade-stiffened panels with circular cutouts is predicted using Finite Element Analysis. In this optimization, the design variables were the cutout size, cutout location, fiber orientation angles, number and locations of stiffeners. Three types of in-plane loading were considered; namely, uniaxial, biaxial and shear loading. Based on the model studies, the total increase in the buckling load due to the presence of cutouts and stiffeners can reach up to 5 times in uniaxial loading, 7 times in biaxial loading and 2 times in shear loading compared to perfect plates. Several other imperative findings are identified based upon the various parameters influencing the buckling behavior. Guidelines for the optimal stiffeners' configurations and cutouts' proportioning are developed

Experimental and theoretical investigations of spigot connections under cyclic loading

Cyclic load tests were conducted on the spigot connections for a system scaffold. Two different connections were tested, one where both ends of a spigot were bolted to tubes and the other where one end was bolted and the other end welded. The tests were conducted by applying a series of different fixed axial loads together with a variable side load which was increased until failure occurred. The objective of undertaking cyclic tests was to not only obtain the rotational stiffnesses of the connection but also the looseness in the connection as looseness has been shown to reduce the performance of frames, and previous research and experiments involving spigots have ignored these effects. The tests and accompanying finite element calculations showed that the looseness was 0.009 radians for the double bolted spigot and 0.005 radians for the welded connection. The connections proved to be relatively unstable at high axial loads showing considerable scatter in the results. The results were in agreement with the stiffness results obtained by André that for a range of axial loads a single rotational stiffness could be applied but that for low and high axial loads different stiffnesses must be used

Influence of Temperature on Shear Behavior of Lightweight Reinforced Concrete Beams Using Pozzolana Aggregate and Expanded Polystyrene Beads

The innovation inherent to employing expanded polystyrene (EPS) beads lies in its transformative impact on traditional concrete practices. Through the incorporation of EPS beads in concrete mixtures, a novel approach emerges that significantly alters the material’s characteristics, and opens up new avenues for construction and design. Studying the shear behavior of RC beams made with EPS beads is essential for advancing knowledge, improving design practices, ensuring structural integrity, and promoting the effective and responsible use of innovative materials in construction. This research experimentally investigated the effect of using EPS beads and pozzolana aggregate (PA) on the shear behavior of the RC beams. A total of 27 simply supported rectangular beams were cast, using three novel distinct mix designs, and were subjected to two-point load testing until failure. These three mixes were categorized as follows: a control mix, a mix with only EPS, and a mix with EPS, along with an additive. The ultimate failure load was experimentally recorded for all specimens, and the influence of the temperature (300 °C and 600 °C) on the RC beams made with EPS was examined. The findings revealed a reduction in the concrete compressive strength and density in the beams containing EPS and EPS with superplasticizers of (21.7%, 24.9%) and (11.3%, 16.2%), respectively. Additionally, EPS played a significant role in diminishing the ultimate shear capacity of the beams, compared to the control beams, by about 19.4%. However, the addition of a superplasticizer along with the EPS helped to maintain the beam capacity, to some extent. Conversely, the beams exposed to a temperature of 300 °C exhibited an almost similar capacity to that of the control beams without heating. Nevertheless, at 600 °C, the beams displayed a noticeable decrease in the ultimate load capacity, compared to the unheated control beams