Khaled Sennah

Evaluation of impact factors for composite concrete-steel cellular straight bridges

Abstract This paper presents a method for determining the dynamic impact factors for straight composite concrete deck–steel girder cellular bridges under AASHTO truck loading. The bridges are modeled as three-dimensional structures using commercially available software. The vehicle is idealized as a pair of concentrated forces, with no mass, travelling across the bridge. An extensive parametric study is conducted, in which 120 composite multi-cell bridge prototypes are analyzed. The key parameters considered in this study are: number of cells, number of lanes, span length, number and area of cross-bracing and top-chord systems, and truck(s) speed and truck(s) positioning. Based on the data generated from the parametric study, expressions for dynamic impact factors for moment, reaction, and deflection for such bridges are proposed. The results from this practical-design-oriented study would enable bridge engineers to design new composite cellular bridges more reliably and economically. Furthermore, the results can be used to evaluate the load-carrying capacity of existing composite cellular bridges since even a small increase in strength for live load can make the difference between closing a bridge and leaving it open.

Experimental Study on Full-Scale Pretensioned Bridge Girder Damaged by Vehicle Impact and Repaired with Fiber-Reinforced Polymer Technology

AbstractA bridge was damaged when a dump truck violated the height clearance limitation on Highway 401 in Ontario, Canada. The collision caused extensive damage to the AASHTO Type-III precast/prestressed bridge girders, which led to the closure of the two-lane bridge. Crack mapping showed extensive torsion-shear cracks between the girder quarter points, horizontal crack at the flange-web junctions, and spalled concrete at point of impact. Preliminary elastic testing on the girder established that the flexural capacity of the girder had not been significantly affected. As such, flexural strengthening was not necessary. Crack patterns and severity, followed by analysis, have shown that the girder is deficient in shear capacity. Therefore, the girder was strengthened for shear throughout its entire length using carbon fiber–reinforced polymer (CFRP) sheets. This paper presents a summary of the design and detailing of the elastic behavior test conducted before repair, the girder repair methodology, and result...

Parametric effects on the performance of traffic light poles in vehicle crashes

Abstract Collisions between vehicles leaving the road and unforgiving roadside objects (trees, poles, road signs, and other street furniture) are a major road-safety problem. The severity of these collisions depends in part on the incompatibility of vehicle-to-roadside hardware. The literature review shows that a few finite element computer simulation attempts have been conducted using existing traffic roadside hardware, without further research to enhance their safety performance against vehicle impacts. The aim of this research is to contribute to the efficient design of traffic light poles involved in vehicle frontal collisions by developing an experimentally calibrated, computer-based, finite element model capable of capturing all impact characteristics. This is achieved by using the available nonlinear dynamic analysis software ȁLS-DYNAȁ, which can accurately predict the dynamic response of both the vehicle and the traffic light pole. A parametric study was conducted to evaluate the effects of key parameters on the response of the pole embedded in soil when impacted by vehicles. These parameters included soil type (clay and sand), pole material type (steel and aluminum), embedment length of the pole, and vehicle impacting speed. It is demonstrated from the results of the numerical analysis that the aluminum pole–soil system has favorable advantages over steel poles, where the aluminum pole absorbed vehicle impact energy in a smoother manner, which leads to smoother acceleration pulse and less deformation of the vehicle than those encountered with steel poles. Also, it was observed that clayey soil brings slightly more resistance than sandy soil, which helps in reducing pole movement at ground level. Moreover, results show that the longer the embedment length, the better the intrusion and acceleration of the vehicle.

A study of injury parameters for rearward and forward facing 3-year-old child dummy using numerical simulation

Abstract More children die of road traffic injuries than of any other cause. Nonuse and misuse of child restraints is common and leads to preventable severe injuries or deaths. Furthermore, many children graduate to inappropriate restraint systems or switch from rearward to forward facing prematurely. Facing rearward is intrinsically safer, provided the head is supported, and the reasons for seating a child in the opposite position relate to convenience, not safety. With heavy heads and weak necks, children are vulnerable to catastrophic traction injuries to the cervical cord, and children older than 1 year retain this vulnerability. Most studies have estimated that rearward facing restraints reduce the risk of serious injury by about 80–90%. A recent analysis of the Swedish Volvo crash database reported that the injury reducing effect of rearward facing child restraints might be as high as 96%. However, the age at which children should start sitting in a forward-facing position is controversial. The American Academy of Pediatrics has recently advised that children should be seated facing the rear of the vehicle for as long as possible and at least until 1 year of age. Both Transport Canada and the US National Highway Traffic Safety Administration (NHTSA) currently suggest having children face forward from about 1 year of age or once they reach 10 kg (22 lb), while Australian children are often turned around to forward facing at 5 to 6 months of age. In this paper a multi-body dynamic simulation MADYMO model is developed for rearward and forward facing 3-year-old child dummy. The reasonable correlation between the developed forward facing numerical simulation results and the experimental results indicates that the model is robust. Simulation for both facing configurations is conducted using an experimental moderate frontal crash pulse. The study indicates that the upper neck forces, and the neck injury criteria can be greatly reduced by keeping the child in the rearward facing position. For children safety, parents and caregivers should seriously consider keeping children rearward facing for as long as possible. Moreover, manufacturers should be encouraged to develop car safety seats that accommodate children rear facing up to 4 years of age.

Anchorage Capacity of Concrete Bridge Barriers Reinforced with GFRP Bars with Headed Ends

An experimental program was conducted to investigate the application of headed glass fiber-reinforced polymer (GFRP) ribbed bars at the barrier wall-deck anchorage. Six full-scale barrier models of 1,200 mm in length were erected and tested under static monotonic loading to determine their ultimate load-carrying capacities and failure modes with respect to the barrier wall-deck anchorage. Four PL-2 barrier specimens were cast: two of them were of tapered face and the other two specimens were of parapet type with constant thickness. Each set had a steel-reinforced specimen as the control model and a GFRP-reinforced specimen. In addition, two PL-3 GFRP-reinforced specimens were erected with different spacing of GFRP bars. Each specimen was loaded laterally until collapse. This paper presents the results from these tests in the form of crack pattern, deflection history, and ultimate load-carrying capacity. Experimental results were compared with the design values specified in the Canadian bridge code for barrier anchorage into the deck slabs, showing a large margin of safety for the proposed GFRP-reinforced barriers. In addition, a parametric study was undertaken using finite-element analysis to investigate the applicability of resultant design loads prescribed by the Canadian bridge code for the design of the barrier wall-deck anchorage. The key parameters considered in this study were deck overhang length and thickness and barrier length. The data generated from this parametric study were used to develop set of empirical expressions for the factored applied moment at the barrier-deck interface, as well as the factored tensile force required to design the deck slab cantilever.

Retrofitting Actual-Size Precracked Precast Prestressed Concrete Double-Tee Girders Using Externally Bonded CFRP Sheets

Precast prestressed double-tee (DT) girders are considered a crucial element of modern infrastructure used to accelerate building construction worldwide. These girders can be deficient because of local damages and develop cracks as a result of improper transportation and handling. Therefore, it is very important to develop an efficient retrofitting technique in order to restore the lost capacity and/or even outperform it. The objective of this paper is to develop retrofit strategy of the deficient girders using the externally bonded carbon-fiber-reinforced polymer (EB-CFRP) technique and verify it using field data. A field test was conducted on three actual-size precast pretensioned DT girders having different levels of damage and retrofitted using CFFP sheets. The girder stems for two of them were strengthened in flexure using unidirectional U-shaped CFRP sheets, while all girders were shear-strengthened at their dapped ends. Each girder was loaded incrementally up to collapse while the deflection of the girder and normal strains developed on both concrete surface and the CFRP sheets were recorded at each load increment. Test results assured the adequacy of the adopted strengthening technique with respect to both ultimate capacity and ductility. In addition, the experimental flexural and shear resistances of the retrofitted girders are far greater than those obtained from equations available in design codes by at least 60%.

Curvature Limitations for Slab-on-I-Girder Bridges

In recent years, horizontally curved bridges have been widely used in congested urban areas, where multilevel interchange structures are necessary for modern highways. In bridges with light curvature, the curvature effects on bending, shear, and torsional stresses may be ignored if they are within an acceptable range. Treating horizontally curved bridges as straight bridges with certain limitations is one of the methods to simplify the design procedure. Bridge design specifications and codes have specified certain limitations to treat horizontally curved bridges as straight bridges. However, these limitations do not differentiate between bridge cross section configurations, in addition to being inaccurate in estimating the structural response. Moreover, these specifications were developed primarily for the calculation of girder bending moments. To investigate the accuracy of these limitations, a series of horizontally curved, braced concrete slab-over steel I-girder and slab-on-concrete I-girder bridges were analyzed, using three-dimensional finite-element modeling, to investigate their behavior under dead loading. The major internal forces developed in the members were determined, namely, girder longitudinal bending stresses, vertical deflections, vertical support reactions, and bridge fundamental flexural frequencies for different degrees of curvature, span length, bridge width, and span continuity. Empirical equations for these straining actions were developed as a function of those for straight bridges. The stipulations made in bridge codes for treating a curved bridge as a straight bridge were then correlated with the obtained values from the finite-element modeling. Results proved that such code limitations were unsafe. Based on the data generated from this parametric study, sets of empirical expressions were developed to determine such limitations more accurately and reliably.

Curvature Limitations for Concrete Box-Girder and Solid-Slab Bridges

In bridges with light curvature, curvature effects may be ignored if they are within acceptable range. In contrast to ACI 343R, the Canadian Highway Bridge Design Code, AASHTO Guide Specifications for Horizontally Curved Bridges (American Association of State Highway and Transportation Officials), and AASHTO-LRFD Bridge Design Specifications specify certain limitations to treat a horizontally curved bridge as a straight one in structural design. However, these limitations proved to be inaccurate in estimating the structural response. To investigate the accuracy of these limitations, a series of curved concrete cellular, multi-box, and solid-slab bridge configurations were analyzed in this study using finite element modeling to investigate their behavior under dead loading. The major internal forces developed in the members were determined and then compared with those obtained for straight bridges of identical configuration. The stipulations made in bridge codes for treating a curved bridge as a straight one were proven unsafe when correlated with the finite element analysis (FEA) results. As such, sets of empirical expressions were developed to determine such limitations more accurately and reliably.

Behavior of RC Slab-Column Connections Strengthened with External CFRP Sheets and Subjected to Eccentric Loading

AbstractStrengthening of both aging and modern infrastructure has become necessary as a result of increased load demand and/or to restore the capacity of a member. For example, flat slabs (commonly utilized in parking garages) are subjected to an aggressive environment and increased traffic loads and additionally require strengthening and/or repair. Fiber-reinforced polymer (FRP) sheets and laminates externally bonded to concrete slabs around the slab-column joint are widely used to enhance the strength of flat slabs. Slab-column connections are most often subjected to eccentric loading; however, most reported studies have focused on retrofitted slab-column connections subjected to concentric loads. This paper aims to fill this knowledge gap and experimentally investigate the effect of eccentric loading on the behavior of slab-column connections retrofitted by externally bonded carbon fiber-reinforced polymer (CFRP) sheets. Six full-scale (2,000×1,000×150-mm) interior slab-column connections subjected to ...

Comparative Structural Behaviour of Multi-Cell and Multiple-Spine Box Girder Bridges

Publisher Summary The use of curved box girder bridges in interchanges of modern highway systems has become increasingly popular for economic and esthetic considerations. Composite concrete deck-steel box girder bridges may take the form of single-cell, multi-cell, and multiple-spines. They provide considerable flexural and torsional strengths to resist the applied loads. This chapter discusses three types of curved box-girder bridges of the same material content—namely, braced multi-cell bridge, multiple-spine bridge with internal bracings, and multiple-spine bridge with internal and external bracings among boxes. The finite-element method is used to model the bridges. Shell elements are used to model the concrete deck slab, steel cells, and end diaphragms; while three-dimensional beam elements are used to model top steel flanges and cross-bracings. Comparison of the theoretical values of selected structural quantities, such as support reactions, tangential stresses, and overall load carrying capacity, are presented for the three types of bridges. A comparison of the dynamic characteristics, natural frequencies, and corresponding mode shapes of such bridges is also presented in the chapter. The chapter concludes that curved bridge of cellular cross-section is the most economic section to resist applied loads.