In contemporary society, industrialization and rising of terrorism threats highlight the necessity and importance of structural protection against accidental and intentionally malicious blast loads. Consequences of these extreme loading events are known to be catastrophic, involving personnel injuries and fatalities, economic loss and immeasurable social disruption. These impacts are generated not only from direct explosion effects, that is, blast overpressure and primary or secondary fragments, but also from the indirect effects such as structural collapse. The latter one is known to be more critical leading to massive losses. It is therefore imperative to enlighten our structural engineers and policy regulators when designing modern structures. Towards a better protection of concrete structures, efforts have been devoted to understanding properties of construction materials and responses of structures subjected to blast loads. Reliable blast resistance design requires a comprehensive knowledge of blast ...

Review of the current practices in blast-resistant analysis and design of concrete structures:

Structural optimization using equivalent static loads at all time intervals

Structural Optimization under Equivalent Static Loads transformed from Dynamic Loads based on Displacement

Linear static response structural optimization has been developed fairly well by using the finite element method for linear static analysis. However, development is extremely slow for structural optimization where a non linear static analysis technique is required. Optimization methods using equivalent static loads (ESLs) have been proposed to solve various structural optimization disciplines. The disciplines include linear dynamic response optimization, structural optimization for multi-body dynamic systems, structural optimization for flexible multi-body dynamic systems, nonlinear static response optimization and nonlinear dynamic response optimization. The ESL is defined as the static load that generates the same displacement field by an analysis which is not linear static. An analysis that is not linear static is carried out to evaluate the displacement field. ESLs are evaluated from the displacement field, linear static response optimization is performed by using the ESLs, and the design is updated. This process proceeds in a cyclic manner. A variety of problems have been solved by the ESLs methods. In this paper, the methods are completely overviewed. Various case studies are demonstrated and future research of the methods is discussed.

Technical overview of the equivalent static loads method for non-linear static response structural optimization

The joined wing is a new concept of the airplane wing. The forewing and the aft wing are joined together in a joined wing. The range and loiter are longer than those of a conventional wing. The joined wing can lead to increased aerodynamic performance and reduction of the structural weight. In this research, dynamic response optimization of a joined wing is carried out by using equivalent static loads. Equivalent static loads are made to generate the same displacement field as that from dynamic loads at each time step of dynamic analysis. The gust loads are considered as critical loading conditions and they dynamically act on the structure of the aircraft. It is difficult to identify the exact gust-load profile; therefore, the dynamic loads are assumed to be a one-cosine function. Static response optimization is performed for the two cases: one uses the same design variable definition as dynamic response optimization, and the other uses the thicknesses of all elements as design variables; the results are then compared.

Structural optimization of a joined wing using equivalent static loads

All the loads in the real world act dynamically on structures. Since dynamic loads are extremely difficult to handle in analysis and design, static loads are utilized with dynamic factors. The dyna mic factors are generally determined based on experiences. Therefore, the static loads can cause problems in precise analysis and design. An analytical method based on modal analysis has been proposed for the transformation of dynamic loads into equivalent static load sets. Equivalent static load sets are calculated to generate an identical displacement field in a structure with that from dynamic loads at a certain time. The process is derived and evaluated mathematically. The method is verified through numerical tests. Various characteristics are identified to match the dynamic and the static behaviors. For example, the opposite direction of a dynamic load should be considered due to the vibration response. A dynamic bad is transformed to multiple equivalent static loads according to the number of the critical times. The places of the equivalent static load can be different from those of the dynamic load. An optimization method is defined to use the equivalent static loads. The developed optimization process has the same effect as the dynamic optimization which uses the dynamic loads directly. Standard examples are solved and the results are discussed

Structural Optimization under Equivalent Static Loads Transformed from Dynamic Loads Based on Displacement

Generally, dynamic loads are applied to real structures. Since the analysis with the dynamic load is extremely difficult, static loads are utilized by proper conversions of the dynamic loads. The dynamic loads are usually converted ot static loads by safety foactors of experiences. However, it may increase weight and decrease reliability. In this study, a method is proposed for the conversion process. An equivalent static load is calculated ot generate a same maximum displacement. The method is verified through numerical tests on a spring-mass systems of one and multi degrees-of freedom. It has been found that the duration time of the loads and the natural frequencies of the structures are critical in the conversion process. A road arem is a self-propelled howizer is selected for the application of the proposed method. The shape of the road arm is optimized under the converted static loads.

Transformation of a Dynamic Load into an Equivalent Static Load and Shape Optimization of the Road Arm in Self-Propelled Howitzer

This paper presents a quasi-static optimization technique for elastic structures under dynamic loads. An equivalent static load (ESL) set is defined as a static load set which generates the same displacement field as that from a dynamic load at a certain time. Multiple ESL sets calculated at every time step are employed to represent the various states of the structure under the dynamic load. They can cover every critical state that might happen at an arbitrary time. Continuous characteristics of dynamic load are simulated by multiple discontinuous ones of static loads. The calculated sets of ESLs are applied as a multiple loading condition in the optimization process. A design cycle is defined as a circulated process between an analysis domain and a design domain. Design cycles are repeated until a design converges. The analysis domain gives a loading condition necessary for the design domain. The design domain gives a new updated design to be verified by the analysis domain in the next design cycle. This iterative process is quite similar to that of the multidisciplinary optimization technique. Even though the global convergence cannot be guaranteed, the proposed technique makes it possible to optimize the structures under dynamic loads. It has also applicability, flexibility, and reliability

http://koreascience.or.kr:80/article/JAKO200000618833493.pdf

U-Seok Choe

Papers

Structural Optimization under Equivalent Static Loads Transformed from Dynamic Loads Based on Displacement

Transformation of a Dynamic Load into an Equivalent Static Load and Shape Optimization of the Road Arm in Self-Propelled Howitzer

Quasi-Static Structural Optimization Technique Using Equivalent Static Loads Calculated at Every Time Step as a Multiple Loading Condition