Amjad J. Aref

Vibration characteristics of a fiber-reinforced polymer bridge superstructure

Dynamic response of the first fiber-reinforced polymer composite bridge built in the US was studied using experimental modal tests and validated finite element models. This slab bridge was manufactured with a longitudinal joint, in the form of a shear-key, and was connected in the field using epoxy resins. Long-term performance of such joints is critical for future applications of similar designs. At the same time, the shear-key details are not visible, once joined, and cannot be inspected using routine inspection procedures. Hence, experimental modal analysis was used to evaluate the integrity of the longitudinal joint. A finite element model validated with field test data was developed to further study the effect of the longitudinal joint degradation on vibration characteristics of the structure. The finite element analysis was also used to evaluate the modal-based techniques for future inspections. Results indicate that the longitudinal joint is performing as intended, and only high degradation of the joint can be detected using the measured vibration characteristics of the bridge.

A combined honeycomb and solid viscoelastic material for structural damping applications

The goal of this paper is to investigate the feasibility of a proposed combined polymer composite damping system. A new composite damping system, which consists of a polymer honeycomb and a viscoelastic solid material is introduced. This new system is primarily intended for energy dissipation and vibration control, whereby the combined viscoelastic system serves as an interface layer within lightweight composite panels subjected to in-plane shear. The basic concept and mechanical properties for combining the polymer honeycomb with 3M solid viscoelastic materials are investigated under different strain inputs and frequencies. Subsequently, numerical models are established in which the effect of the temperature and frequency are taken into account. The analysis results given by the simplified numerical modeling agree with the results of the experiment. This study also leads to useful information with respect to the optimum design of the combined damping system.

Design and performance of a modular fiber reinforced plastic bridge

An integral fiber reinforced plastic bridge structural system is described. The design is carefully engineered to incorporate fiber reinforced plastics as the sole structural material. As a result, a number of special features evolved to produce an efficient bridge design. We describe the structural components, highlight the structural performance and some of the novel features incorporated in this design, and compare the performance of our design to other composite bridges. The design appears to have potential as a new approach to the ancient bridge construction problem that utilizes the properties of this class of materials to the fullest.

Quasi-Static Cyclic Testing of a Large-Scale Hybrid Sliding-Rocking Segmental Column with Slip-Dominant Joints

This paper presents the findings of an experimental study that investigated the response properties of segmental cantilever columns incorporating internal unbonded posttensioning (PT) and slip-dominant (SD) joints. The SD joints exhibited controlled sliding that provided energy dissipation with low damage. All joints of these columns, except for the bottom one, were designed to be SD. The bottom joint was designed to be rocking dominant (RD) and exhibited rocking that offered self-centering to the system. Design objectives and equations are presented. These equations were used for the design of a large-scale cantilever column that was subjected to reverse lateral cyclic loading at its top end, reaching a maximum drift ratio of 14.9%. At small drift ratios (≤3%), the response was dominated by sliding of the SD joints that provided energy dissipation (damping). For medium drift ratios (between 3 and 10%), rocking at the bottom joint increased and provided self-centering properties to the system. For large drift ratios (>10%), the self-centering properties decreased, but the damping properties remained practically constant. Rocking at the SD joints remained small at all times. Minor spalling was observed in the SD joints, while concrete crushing was observed at the bottom joint.

An optimization design procedure for fiber reinforced polymer web-core sandwich bridge deck systems

Abstract The development of optimization design procedures has emerged as an essential component primarily to overcome the challenge of high initial construction costs associated with the fiber reinforced polymer (FRP) bridge deck systems. This paper devises a genetic algorithm-based optimization procedure to minimize the weight of FRP web core sandwich bridge deck systems. A Ritz-based simplified analysis method is applied to couple with the proposed optimization procedure as the structural analysis engine. The design procedure involves the parallel optimal search of mixed continuous and discrete parameters––geometrical parameters, sandwich configuration and material architecture––for the whole sandwich structure. A novel data structure is proposed for the genetic representation in a one-gene-one-variable format. Consequently, specific genetic operators are tailored to accommodate the nonstandard data structure. A problem-independent scheme that does not require any penalty parameter is developed to handle the design constraints. The resulting design procedure provides an effective optimal design framework for the preliminary design stage before performing detailed finite element analysis.

Ambient vibration and seismic evaluation of a cantilever truss bridge

Abstract An experimental ambient vibration field investigation with a companion computational modeling study of a cantilever truss bridge is presented. The ambient vibration experiments were conducted on the central suspended span and two adjacent anchor spans of the North Grand Island (NGI) Bridge. Three-dimensional finite element model of the bridge is validated against the experimental results. Results from time history analyses using selected ground motions are used to assess the damage threshold of the bridge. A nonlinear static procedure using the capacity–demand spectrum approach is then employed to evaluate the expected seismic performance of the structure. Results show that sway frame members are especially prone to damage under earthquake-induced deformations. However, overall response of the structure may be considered satisfactory from a life safety standpoint.

SEISMIC PERFORMANCE AND RETROFIT OF STEEL PILE TO CONCRETE CAP CONNECTIONS

This paper looks at the seismic-performance of steel pile-to-pile cap connections representative of construction practice in the eastern U.S. Two perspectives are considered. The first is the seismic vulnerability of existing pile cap connections, where the embedment depth of the pile inside the cap beam is small. An initial experimental study, therefore, was conducted for testing 2 specimens that represented existing exterior connections under cyclic lateral loading. The second perspective is the seismic design requirements for strong cap beam-to-pile connections. Hence, a theory assuming a linear distribution of stresses along the connection embedment depth was developed, and comparisons with a finite element model were performed. A second experimental program was conducted to evaluate the performance of specimens retrofitted in accordance with the theoretical model developed in this study. Results of the second experimental study validated the proposed retrofit strategy.

Interaction Curves for In-Plane and Out-of-Plane Behaviors of Unreinforced Masonry Walls

Different types of macro-elements have been proposed to simulate the behavior of unreinforced masonry (URM) structures under seismic loads. In many of these, macro-elements URM walls are replaced with beam elements with different hysteretic behaviors. The effect of out-of-plane loading or change of gravity load due to the overturning moment is usually not considered in the behavior of these macro-elements. This article presents interaction curves for bidirectional loadings of unreinforced masonry walls to investigate the importance of these factors. Two parameters are systematically changed to derive the interaction curves for a wall with specific dimensions, including compressive traction atop the wall to represent gravity loading, and loading angle that represents a combination of in-plane and out-of-plane earthquake loadings. Interaction curves are developed considering various possible failure modes for bricks and mortar, including tension, crushing and a combination of shear and compression/tension failures. The proposed interaction curves show the initiation of failure of URM walls as a function of compressive traction and loading angle. Several examples are presented for URM walls with different aspect ratios to aid in understanding the effects of various parameters on the derived interaction curves. Finally, for a specific case, the derived interaction curve is compared with nonlinear finite element results and ASCE41. The results show that, as a simplified method, the derived interaction curves can be used for the preliminary evaluation of URM walls under bidirectional loadings.

Experimental Seismic Performance of a Hybrid Sliding–Rocking Bridge for Various Specimen Configurations and Seismic Loading Conditions

AbstractThis paper presents the major findings of a shake table testing program on a large-scale (1:2.39) novel segmental concrete single-span bridge specimen. Emphasis is given on various specimen configurations and seismic loading conditions. The bridge specimen, termed hybrid sliding–rocking bridge, incorporated a box-girder superstructure with rocking joints and internal unbonded posttensioning (PT), and two single-column piers with internal unbonded PT. The pier columns included end rocking joints and intermediate sliding joints along the column height. Various configurations of the bridge specimen were considered with respect to the seismic mass and the superstructure-to-substructure connectivity. These configurations were subjected to far-field (F-F) and near-fault (N-F) ground motion ensembles scaled to various seismic hazard intensities. Asynchronous support excitation was also considered. The testing program included approximately 145 seismic tests. The dynamic response of the specimen was found...

Sustained-Load and Fatigue Performance of a Hybrid FRP-Concrete Bridge Deck System

The design and construction of bridge systems with long-term durability and low maintenance requirements is a significant challenge for bridge engineers. One possible solution to this challenge could be through the use of new materials, e.g., fiber-reinforced polymer (FRP) composites, with traditional materials that are arranged as an innovative hybrid structural system where the FRP serves as a load-carrying constituent and a protective cover for the concrete. This paper presents the results of an experimental investigation designed to evaluate the performance of a 3/4 scale hybrid FRP-concrete (HFRPC) bridge deck and composite connection under sustained and repeated (fatigue) loading. In addition, following the sustained-load and fatigue portions of the experimental study, destructive testing was performed to determine the first strength-based limit state of the hybrid deck. Results from the sustained-load and fatigue testing suggest that the HFRPC deck system might be a viable alternative to traditiona...