Effect of fully restrained beam-to-column connection on the progressive collapse strength of steel moment frames

The beam-to-column connection has been identified as a key element for steel frame structures to maintain the structural integrity during progressive collapse phenomenon. In the current study, in order to assess the effects of beam-to-column connection type on the progressive collapse strength of steel moment frames, the progressive collapse behavior of a steel intermediate moment frame structure was evaluated with 10 different types of fully restrained connections. The progressive collapse strength of these buildings against sudden removal of a column was separately studied using nonlinear static alternate path method presented in Unified Facility Criteria progressive collapse guideline. To consider the nonlinear effects in the structural modeling, plastic hinges for beam and column members and connections were defined and modeled according to the ASCE 41 standard. The results of the progressive collapse analyses indicated that if the plastic hinges of connections are separately defined in addition to the plastic hinges of beams and columns, the structure will have lower progressive collapse strength, and the calculated dynamic increase factor will grow. Among the studied types of connections, the free flange connection had the best performance and the highest strength against progressive collapse.

Remaining capacity estimation for buildings after an explosion using the adaptive alternate path analysis

After an explosion, determining the remaining capacity of a structure to resist a progressive collapse can provide valuable information for emergency operations and decision makers. Condition assessments after a blast are commonly performed with a visual inspection. However, visual inspections can be time-consuming and involve putting additional personnel into harm’s way. Analytical blast analyses can estimate a structures post-blast condition, but to achieve a high level of accuracy these analyses can be time-consuming and require information regarding the blast event which may not be available at the time. This presents a need for a threat independent post-blast analysis method, which can assess for the post-blast structural condition without requiring personnel to enter the structure. The alternate path method has been used to design buildings to resist a progressive collapse; however, it does not incorporate damage outside of element failure making it unsuitable for post-blast condition assessments. Model updating using modal properties from vibration measurements has been used in structural health monitoring to estimate damage on structures, but it has not been applied to post-blast structures. In this article, a method to estimate the remaining elemental structural capacity of a post-blast structure, called the adaptive alternate path analysis, is presented. This method involves using the alternate path method to assess an updated numerical model, which incorporates the buildings’ structural damage. To demonstrate the impact of incorporating additional damage beyond elemental failure on a structure’s capacity, a simulated study is presented using simulated stiffness reductions. A blast simulation is then used to show the capacity of the updated numerical model to represent the post-blast structure and the improvements gained over using the original model. The presented methodology can be used to assess a structures potential for progressive collapse after a blast, leading to safer emergency operations.

Analysis on Dynamic Response of Reinforced Concrete Frame for Resisting Progressive Collapse

In order to investigate the dynamic response of reinforced concrete spatial frames caused by initial damages, a six-story frame model is analyzed by employing the nonlinear dynamic methodology in accordance with the alternate path method issued by General Services Administration. In this paper, the fiber model and force-based beam-column element are utilized in OpenSees. Four various scenarios are separately analyzed with incremental dynamic analysis. It is shown that the model does not collapse and the internal force redistribution mainly appears in the components adjacent to the failure column. The model has the worst capacity to resist progressive collapse in the inner column demolition scenario. It is observed that the plastic hinges mainly concentrate on the beam ends of the failure bay at the beginning of the demolition of columns. Several plastic hinges emerge at the top-floor beam ends of some other bays in latter period. The number of plastic hinges in columns is much less than that in beams, which corresponds to the design principle ‘strong column and weak beam’.

Progressive Collapse Analysis of CFST Frame with Semi-Rigid Connection

A finite element method was developed to investigate the semi-rigid connection mechanical behaviors in the process of CFST structures progressive collapse, and different semi-rigid connection joint stiffness were taken into consideration and compared to rigid connection. Nonlinear static and dynamic analysis were carried out with alternate path method. The numerical result shows that the increase of joint stiffness would evidently enhance the structural progressive collapse resistance performance, and CFST structures have excellent characteristic to prevent progressive collapse, the great deformation capacity and energy dissipation ability of semi-rigid connections are advantageous to progressive collapse resistance.

Study on Collapse Numerical Simulation Method of Frame Structures Based on Explicit Dynamics

According to the theory of collapse numerical simulation, the explicit finite element algorithm based on explicit dynamics was chose as the numerical calculation method. And combined with the plane RC frame collapse test and the example of ten layers frame structure, the wire frame model, integrated model and separate model were established and the alternate path method was adopted to study the simulate method of structural collapse. With the comparison of several aspects to the results, the rationality of the numerical simulation method and the applicability of the numerical models were verified respectively. At the same time, according to the complex pre-treatment process to the numerical simulation of structural collapse, an MFC program with the function of exporting APDL file which can generate wireframe models for structural collapse simulation in ANSYS/LS-DYNA was developed using VC++ language with the purpose of offering convenience to the numerical simulation process of structure collapse.

Key Components for RC Frame Structure during Progressive Collapse

To illustrate the changes of important components during progressive collapse, this paper sums up the judgment method for important components. Based on the alternate path method and the concept of sensitivity analysis, we determine the key component of a RC frame structure. Then the changes of important components during progressive collapse are given. The results show that the location of key components changing with the structure damage in the process of progressive collapse.