Abstract:
An analytical along with numerical analysis has been carried out to investigate the behavior of concrete simply supported beams strengthened with Fiber-Reinforced Polymer (FRP) unidirectional laminates under impact loading. Concrete beams are reinforced with a minimum ratio of exural and shear steel rebars and nally retrotted with epoxy-bonded high strength carbon FRP laminates in their exure surfaces. The impact force was applied with a solid steel cylinder drop weight. Analytical results showed that composite laminates externally bonded to reinforced concrete beam substrate can signicantly enhance the performance of theses structural members to resist impact loadings. Also, based on the obtained results, in retrotted beams the crack propagation happens in a desirable mode

an increasing of yielded rebar zones and residual beam stiness. Retrotted beams were stier than unretrotted ones in their rst impact response. The residual stiness of impacted concrete beams depends on their initial stiness and the impact energy level. The analytical method uses an idealized elastic spring-mass model and exural wave propagation theory to calculate the dynamic response of assumed beams. Analytical responses are adjusted due to an inelastic response, and nally are used for the simplied designation of impact resisting reinforced concrete beams retrotting laminates.

Keywords:
Impact loading
Reinforced concrete beam
Composite laminate
Retrotting
FEM.

Abstract:
An FE model of a pedestrian lower legform impactor has been developed and certied, both statically and dynamically, based on EEVC-WG17 requirements. The legform is then utilized in a series of 40 km/hr pedestrian accident analyses to assess the protection level delivered by a typical sedan vehicle. The values of maximum tibia acceleration, maximum knee bending angle, and maximum knee shearing displacement have been extracted for 25 dierent accident congurations and compared with their admissible ranges. It has been shown that tibia acceleration is mainly in uenced by extension of the area transferring the impact load between the legform and the vehicle. However, variations of vehicle front-end structure geometry and stiness in the vertical direction have been found to be the most decisive parameters in the level of legform knee maximum bending rotation and maximum shearing displacement.

Keywords:
Pedestrian accident

Lower extremity injury
Bumper design.

Abstract:
The Endurance Time (ET) method is a new dynamic pushover procedure in which structures are subjected to gradually intensifying acceleration functions and their performance is assessed based on the length of the time interval that they can satisfy required performance objectives. In this paper, the accuracy of the Endurance Time method in estimating average deformation demands of low and medium rise steel frames using ETA20f series of ET acceleration functions has been investigated. The precision of the ET method in predicting the response of steel frames in nonlinear analysis is investigated by considering a simple set of moment-resisting frames. An elastic-perfectly-plastic material model and a bilinear material model with a post-yield stiness equal to 3% of the initial elastic stiness have been considered. For frames with an elastic-perfectly-plastic material model, which are P 􀀀
sensitive cases, the ET analysis for the maximum interstory drift ratio somewhat underestimates the nonlinear response history analysis results. The dierence between the results of the ET analysis and the nonlinear response history analysis for the material model with 3% post-yield stiness is acceptable. The consistency of the base shears obtained by the two methods is also satisfactory. It is shown that, although the results of the ET analysis are not exactly consistent with the results of ground motions analysis, the ET method can clearly identify the structure with a better performance even in the case of structures with a relatively complicated nonlinear behavior.

Keywords:
Nonlinear response history analysis

Dynamic pushover
Endurance time method; Performance-based seismic engineering.

Abstract:
Earthquakes in megacities such as Tehran and Los Angeles pose huge risks that could jeopardize national prosperity and social welfare. Quantifying urban seismic risk is a dicult problem because it requires detailed knowledge of the natural and the built environments, as well as an understanding of both earthquake and human behaviors. Risk assessments can be improved through international collaborations that combine the expertise of earthquake scientists and engineers. The most eective strategies are seismic safety engineering, enforced through stringent building codes and disaster preparations informed by realistic scenarios of large earthquake cascades. These strategies rely on the ability to forecast earthquakes and their eects and to monitor earthquake cascades in near real time. The practical problems of risk reduction are, thus, coupled to the basic problems of earthquake system science: the interseismic dynamics of fault systems and the coseismic dynamics of fault rupture and groundmotion excitation. In the United States, the Southern California Earthquake Center (SCEC) coordinates an extensive research program in earthquake system science, which includes major eorts to improve time-dependent earthquake rupture forecasts through better understanding of earthquake predictability and to develop attenuation relationships that correctly model the physics of seismic wave propagation. Earthquake system science relies on the premise that detailed studies of fault systems in dierent regions can be synthesized into a generic understanding of earthquake phenomena. Achieving such a synthesis will depend on international partnerships that facilitate the development and comparison of well-calibrated regional models, and it will require the deployment of a cyberinfrastructure that can facilitate the creation and ow of information required to predict earthquake behavior. In the not-too-distant future, we will be able to incorporate much more physics into seismic hazard and risk analysis through physics-based, system-level simulations.

Keywords:
Seismic risk analysis

Risk assessment
Earthquake prediction
Seismic wave propagation.

Abstract:
An ecient methodology is proposed to optimize space trusses considering geometric nonlinearity. The optimization task is performed by a continuous Particle Swarm Optimization (PSO). Design variables are cross sectional areas of the trusses and their weights are also taken as the objective function. Design constraints are dened to restrict nodal displacements and element stresses and prevent the overall elastic instability of the structures during the optimization procedure. In order to reduce the computational eort of the optimization process, an Adaptive Neuro Fuzzy Inference System (ANFIS) is employed to approximate the nonlinear analysis of the structures instead of performing via a time consuming Finite Element Analysis (FEA). The presented ANFIS is compared with a Back Propagation Neural Network (BPNN) and appears to produce a better performance generality for evaluating structure design values. Test example results demonstrate the computational advantages of the suggested methodology for optimum design of geometrically nonlinear space trusses.

Keywords:
Space truss

Geometric nonlinearity
Particle swarm optimization
Approximation concepts; Adaptive neuro fuzzy inference system.