Seismic assessment of hollow core concrete bridge piers

Hollow core concrete bridge piers are traditionally believed to be vulnerable to seismic action. However, the seismic vulnerability of such piers has not been investigated fully. In this paper, an analytical model to assess seismic vulnerability of hollow core concrete bridge pier is developed. The model is validated with available experimental results. Code recommendations for hollow core bridge piers are evaluated. It is shown that confinement reinforcement requirements in the codes are sometimes highly conservative and sometimes non-conservative. However, the recently developed confinement reinforcement equations for solid bridge piers at Sherbrooke University can be applied for economic and safe design. It is demonstrated that hollow core bridge piers are not as vulnerable as it is traditionally believed. Such piers can attain expected ductility, if designed properly

Optimal target performance for cost-effective seismic design of bridges

A systematic approach is proposed for evaluating the cost-effectiveness of existing bridge design codes from the perspective of lifecycle cost consideration. In the life cycle cost formulation, costs of construction, damage cost, road user cost, as well as discount cost over the design life of the bridge are considered. The optimal performance is selected on the basis of minimum life cycle cost. The performance of a typical two-span bridge designed according to a current code provision for different earthquake ground motion levels is predicted and optimal target performance is selected based on life cycle cost with different assumptions of user cost. It is demonstrated that life cycle cost should be considered in the design phase of a new structure or of a structure to be retrofitted, and the target performance significantly depends on the expected average daily traffic using the road

Seismic vulnerability of hollow core concrete bridge piers

Hollow core concrete bridge piers are traditionally believed to be vulnerable to seismic action. However, seismic vulnerability of such piers has not been investigated fully. In this paper, a modeling method to assess seismic vulnerability of hollow core concrete bridge pier is developed. The method is validated with available experimental results. Code recommendations for hollow core bridge piers are evaluated. It is shown that confinement reinforcement requirements in the codes are sometimes highly conservative and sometimes non-conservative. However, the recently developed confinement reinforcement equations for solid bridge pier at Sherbrooke University can be applied for economic and safe design. It is demonstrated that hollow core bridge piers are not as vulnerable as it is believed traditionally. Such piers can attain expected ductility, if designed properly

Optimal performance for cost effective seismic design of bridges

A systematic approach is proposed for evaluating the cost-effectiveness of existing design codes from the perspective of lifecycle cost consideration. In the life cycle cost formulation, cost of construction, damage cost, road user cost, as well as discount cost over the design life of the bridge are considered. The optimal performance is selected on the basis of minimum life cycle cost. The performance of a typical two-span bridge designed according to a current code provision for different earthquake ground motion levels is predicted and optimal target performance is selected based on life cycle cost with different assumptions of user cost. It is demonstrated that life cycle cost should be considered in the design phase of a new structure or of a structure to be retrofitted, and the target performance significantly depends on the expected average daily traffic for the road

Confinement reinforcement for bridges in medium to high seismicity zone based on new CSA A23.3-04 approach

Recent advances in confinement reinforcement of building columns have resulted in changes in Canadian code for Design of Concrete Structures CSA A23.3-04. Bridge columns and piers may also take advantage of these advances. The purpose of this paper is to use a comparable approach to propose new equations to be introduced in future Canadian bridge design code. The adopted approach for transverse reinforcement is based on the recently developed uniaxial confinement model for concrete column at Sherbrooke University. Parametric studies have been carried out on some typical bridge columns and piers to develop equations for confinement reinforcement. An intermediate level of ductility (moderate ductility) for bridge columns and piers has been introduced, similar to that in CSA A23.3-04 building design code. Confinement reinforcement for this level of ductility has been found to be less stringent than that for ductile level. This level of ductility is suitable for regions of low to medium seismicity. The adopted approach is supported by experimental results and will provide the designer more flexibility but economical and safer seismic design of bridge columns and piers

Seismic performance of bridges designed according to AS 5100

Bridges are the critical components of a nation's transportation system, as closure of an important bridge in the event of an earthquake can disrupt the total transportation network. In Australian standard for bridge design, ASBD (AS 5100-2004), consistent with other major bridge design codes (for example, AASHTO in the USA and CAN/CSA-S6 in Canada), bridges are classified according to their importance levels. The anticipated performances (performance objectives) of the bridges in small to moderate (Return Period, RP= 100 years), design level (RP= 500 years) and large (RP=2500 years) earthquake events have been specified in major bridge design codes, although not explicitly stated in ASBD for bridge design. It is believed that similar performance objectives should also be anticipated for the bridges designed for different importance levels according to ASBD. However, there appears to be no requirement in the code to check whether such multiple performance objectives have been achieved for the designed bridge.Also, no engineering parameters have been assigned to the anticipated performance objectives. This paper correlates seismic performance objectives (both qualitative and quantitative) with engineering parameters which are based on the data collected from available experimental investigations and field investigations from recent earthquakes. A simple methodology has been developed and validated with experimental results for assessing the performance of bridges designed according ASBD. It has been found that the design rules prescribed in ASBD do not guarantee that intended multiple seismic performance objectives can be obtained. Implicit seismic design rule in the form of Performance Response. Modification Factor (PRMF) has been outlined for performance based seismic design of bridges. The implicit design rule has the potential for further development in order to be incorporated in the next generation ASBD

Definition of a VR-based protocol to treat social phobia

Social phobia is an anxiety disorder that is accessible to two forms of treatment yielding scientifically validated results: drugs and cognitive-behavioral therapies. Graded exposure to feared social situations is fundamental to obtain an improvement of the anxious symptoms. Traditionally, exposure therapies are done either in vivo or by imagining the situations. In vivo exposure is sometimes difficult to control and many patients have some difficulties in using imagination. Virtual reality (VR) seems to bring significant advantages. It allows exposures to numerous and varied situations. This paper reports the definition of a clinical protocol whose purpose is to assess the efficiency of a VR therapy compared to a CBT and to the absence of treatment for social phobic patients. It explains the illness' diagnosis and its usual treatments. It exposes all the architecture of the study, the assessment tools, the content and unfold of the therapy sessions. It finally reports first results of a clinical trial in a between-group design in 10 patients suffering from social phobia. The virtual environments used in the treatment reproduce four situations that social phobics feel the most threatening: performance, intimacy, scrutiny and assertiveness. With the help of the therapist, the patient learns adapted cognitions and behaviors with the aim of reducing her or his anxiety in the corresponding real situations. The novelty of our work is to address a group of situations that the phobic patient is most likely to experience and to treat patients according to a precise protocol

Virtual reality therapy versus cognitive behavior therapy for social phobia: A preliminary controlled study

Social phobia is one of the most frequent mental disorders and is accessible to two forms of scientifically validated treatments: anti-depressant drugs and cognitive behavior therapies (CBT). In this last case, graded exposure to feared social situations is one of the fundamental therapeutic ingredients. Virtual reality technologies are an interesting alternative to the standard exposure in social phobia, especially since studies have shown its usefulness for the fear of public speaking. This paper reports a preliminary study in which a virtual reality therapy (VRT), based on exposure to virtual environments, was used to treat social phobia. The sample consisted of 36 participants diagnosed with social phobia assigned to either VRT or a group-CBT ( control condition). The virtual environments used in the treatment recreate four situations dealing with social anxiety: performance, intimacy, scrutiny, and assertiveness. With the help of the therapist, the patient learns adapted cognitions and behaviors in order to reduce anxiety in the corresponding real situations. Both treatments lasted 12 weeks, and sessions were delivered according to a treatment manual. Results showed statistically and clinically significant improvement in both conditions. The effect-sizes comparing the efficacy of VRT to the control traditional group-CBT revealed that the differences between the two treatments are trivial