Dynamic response and behavior of reinforced concrete slabs under impact loading

Reinforced concrete slabs are among the most common structural elements. In spite of the large number of slabs designed and built, the effect of their details on their behavior under impact loads are not always appreciated or properly taken into account. This experimental study was aimed at understanding the dynamic behavior of structural concrete slabs under impact loading to improve the state of the art of protective design. This study investigated the effects of different types of slab reinforcements and the applied impact loads on the dynamic response and behavior of reinforced concrete slabs.     

Blast-resistant structural concrete and steel connections

A series of numerical studies were conducted on the behavior of structural concrete and structural steel connection subjected to blast loads. These studies gradually enhanced the understanding of the role that structural details play in affecting the behavior. Observations from those studies highlighted possible safety concerns with current blast design procedures. Conclusions and recommendations are provided for correcting the observed problems.     

Mesh, gravity and load effects on finite element simulations of blast loaded reinforced concrete structures

The behavior and design of reinforced concrete blast resistant structures are supported by intensive numerical simulations, and the effects of various parameters on the results is of great interest. Finite element simulations were performed in the nonlinear dynamic domain with modified concrete and steel constitutive models. Ten different cases were implemented, each with different reinforcement details. In addition, each case included both a coarse mesh and a fine mesh to determine the effects of mesh resolution on the numerical simulations. Gravity and loading conditions were altered to investigate their influences on the results. Deformations and stress distributions in both the concrete and steel were examined to determine the composite structural behavior and the extent of predicted damage for the various cases. The observations from these analyses highlighted relationships between the simulation parameters and the corresponding outcome. Conclusions and recommendations are presented that could assist in the development of efficient numerical simulations in this general area.     

Accuracy of the finite element method near a curved boundary

Solutions of problems by the finite element method, when curved boundaries are present in the model, may not be accurate. Such a difficulty arises when straight-line elements are used to approximate the curved boundary. This behavior is known in the literature as the “Babuska Paradox”. Despite the fact that the problem has been recognized since the mid 60's, and methods to overcome it have been used quite successfully, many textbooks still ignore it. Here, this “paradox” is demonstrated by plane-stress problems, to which analytical results exist. One known method (the isoparametric element) is used to show how to overcome these difficulties.     

Load–impulse characterization for steel connection

Abnormal loading generated by blast or impact may cause local damage in a building that may evolve to affect the whole structural system. Therefore, structures have to be designed to prevent such disproportional consequences. Connection is an important contributor to ductility and robustness of the structural steel systems in mitigating such consequences. The aim of this study was to derive a better understanding of how steel connections behave under high-speed loads by means of characterizing their resistance, ultimate strength, and ductility in the form of load–impulse diagrams. The established high-strain-rate resistance properties were applied into simplified frame analyses. The accuracy and cost-effectiveness of the approach were then evaluated comparing the results from detailed and simplified models.     

Development of an expert system for preliminary risk assessment of existing concrete dams

The paper presents an expert system to assist in the field inspection of existing concrete dams within the context of a preliminary risk assessment. The paper describes the engineering knowledge and reasoning required to conduct a deterministic field evaluation of the structural stability of the dam. The symptoms and failure modes identified by the expert system along with the required knowledge and procedures are organized in a structured knowledge tree. The instantiation of the frames and firing of the rules for each consultation traces part of the inference tree contained in the structured knowledge tree. Interaction between nearly decomposable problems are executed with metaknowledge procedures, shared rule groups, and active values. Examples are provided.     

A comprehensive R&;D Approach for Critical Infrastructure Protection

This paper provides background on requirements, capabilities and research recommendations for protecting critical infrastructure systems. These activities are needed to develop much more effective solutions to problems that can be currently addressed primarily with conservative, and/or empirical approaches. The expected contributions will have a profound effect on national and international defense and security. Although essential work must be conducted in several important areas, this paper is primarily focused on scientific and technical issues.     

An Intelligent Evacuation,Rescue and Recovery Concept

Recent terrorist incidents have demonstrated that personnel responsible for decision-making in post-attack and structural fire evacuation, rescue and recovery (ERR) activities can significantly benefit from an expert decision support system. In this paper, a concept is proposed for such an expert system that, through the use of sensor technology, can permit real-time assessment of the extent of blast and fire damage to a building, can recommend immediate actions that can be taken to mitigate the situation and prevent further deterioration, can monitor the growth and spread of fire and smoke, and can be used to aid the rescue workers and evacuees in rescue efforts and safe egress. This comprehensive system, once fully operational, can be used for training, blast damage assessment (BDA), target vulnerability assessment (TVA), pre-event emergency preparedness planning, and post-attack ERR operations. The key capabilities of this system stem from the electronic integration of two critical components: a near real-time intelligent BDA/TVA tool and on-line ERR-related optimization techniques. The implementation of this concept will support faster and more efficient evacuation of a building, ship, or other large structure in the event of military attack, fire, natural disaster, chemical attack, discovery of hazardous materials or biological agents, or other circumstances warranting quick escape.     

Simplified analysis of buried reinforced concrete arches under simulated nuclear loads

An approximate analytical approach is modified and applied for the study of shallow-buried reinforced concrete arches under severe dynamic loads. The approach contains a closed form solution for wave propagation in soil, transfer functions for simulation of soil-structure interaction, and a layered beam finite element for representing the structure. Several modifications were incorporated in the original approach, for improving the applied loads and for insuring cross-sectional equilibrium in the analysis. The approach has been used for the investigation of four structures that were tested previously by other researchers, and the numerical results were compared with experimental data and corresponding solutions from advanced numerical codes. The results represented reasonably well the general behavior of the structures under consideration, but several serious limitations of the proposed approach were noted. The comparison between experimental and numerical results provided useful observations on the effectiveness of this approach, and recommendations were presented for future applications.