Dichuan Zhang

Integrated Analytical and Experimental Research to Develop a New Seismic Design Methodology for Precast Concrete Diaphragms

AbstractA new seismic diaphragm design methodology has been developed for precast concrete floor diaphragms. The knowledge required to create the design methodology was obtained through an integrated analytical and experimental research project using two Network for Earthquake Engineering Simulation (NEES) equipment sites. The activities of the project involved a sequence of integrated research tasks that systematically developed knowledge about diaphragm behavior from the reinforcement detail level to the structural system level. These tasks included the use of state-of-the-art experimental techniques made possible through the NEES facilities including hybrid simulation and large-scale shake table tests. Such techniques were crucial to the research as the complex behavior of precast diaphragms is not well described by simple analytical models or idealized experiments. Valuable industry oversight in the planning, execution, and technology transfer stages of the project guided the research activities, incl...

Experimental evaluation of pretopped precast diaphragm critical flexure joint under seismic demands

Precast concrete diaphragm seismic response is examined in experimental research integrating model-based simulation with physical testing. The experimental substructure is the diaphragm critical flexural region of a prototype precast parking structure. This region is expected to undergo significant inelastic flexural deformation, while potentially nonductile regions remain elastic on the basis of capacity design rules from an emerging design methodology. The physical test is conducted at half-scale. The test specimen is detailed using diaphragm reinforcement intended to meet deformability requirements. Predetermined displacement histories are applied to the test specimen on the basis of nonlinear transient dynamic analyses of the prototype structure. The loading history is applied by a test fixture capable of simultaneously providing shear, axial, and moment to the joint. Moment strength, stiffness, rotational deformation capacity, and progressive damage are examined under a sequence of increasing intensity earthquakes. Design recommendations are provided.

Effect of Spandrel Beam to Double Tee Connection Characteristic on Flexure-Controlled Precast Diaphragms

Precast spandrel beams are often used on the perimeter of precast buildings to support the precast floor units. These elements are typically not considered part of the lateral force resisting system. However, the presence of the spandrel beams in the floor system may modify the strength, stiffness, and deformation capacity of the precast floor diaphragm. The nature of this response is highly dependent on the characteristics of the details connecting the spandrel to the precast floor system. These details are often welded connections used primarily for erection stability and designed without diaphragm action in mind. With emerging design methodologies for precast diaphragms requiring better-defined performance, the impact of the spandrel beams must be accounted for. Accordingly, analytical research is presented here that examines the effect of spandrel-beam-connecting details on the global characteristics and local demands of a flexure-controlled precast floor diaphragm. Design recommendations are provided.

Development of diaphragm connector elements for three-dimensional nonlinear dynamic analysis of precast concrete structures

Diaphragm connector elements were developed for three-dimensional finite element models of precast concrete structures used in nonlinear time history analyses. The use of discrete elements for the diaphragm connectors permits the direct evaluation of local force and deformation demands, information needed in calibrating design factors for a new diaphragm seismic design methodology. This article describes the element formulation. The connector elements consist of assemblages of standard elements readily available in most finite element software libraries. The connector element calibration is based on full-scale testing of common precast diaphragm connectors. In these tests, the connector exhibited hysteretic pinching, stiffness/strength degradation, and slip mechanisms. The diaphragm connector elements were constructed to capture these behaviors to an accuracy sufficient for establishing viable design factors, while still appropriate for insertion into large degree-of-freedom models. The models are validated against the results of simulation-driven tests for critical precast diaphragm joints and a half-scale shake table test.

Inertial force-limiting anchorage system for seismic resistant building structures

An innovative floor anchorage system is under development for seismic-resistant buildings. The anchorage possesses a predefined “cut-off” load to limit inertial forces, transforming seismic demands into relative displacement of the floor system with respect to the primary vertical elements, and dissipating seismic energy in the building system. Elastic restoring, stabilizing, and re-centering elements complete the inertial force-limiting anchorage system (IFAS). The system has the potential to limit diaphragm forces, thereby lowering floor accelerations and reducing seismic demands on the lateral force resisting system, resulting in less damage to the structure, non-structural elements and building contents. The IFAS concept is being developed in a multi-university research project including meetings with design consultants for prototype development, computational simulation to optimize design parameters, full-scale component testing to determine prototype characteristics, and a half-scale shake table test to demonstrate the concept. This paper summarizes these efforts to date.

Experimental evaluation of seismic response for reinforced concrete beam–column knee joints with irregular geometries

Regular reinforced concrete beam–column knee joints are typically framed by beams and columns with similar heights. However, complexities in modern architecture layouts may result in irregular geometries for the knee joint. The irregular geometry refers to significant differences in the height for the beam and the column framing into the joint. For example, the height of the beam is considerably larger than that of the column, and vice versa. Seismic performance and behavior for the regular knee joint have been well examined through previous experimental research. However, the knee joint with irregular geometry (termed here as irregular knee joint) may have different seismic behaviors compared to the regular knee joint because the irregular geometry can produce different demands, stiffness, strength, and reinforcing bond conditions. Therefore, this article evaluates seismic behavior of the irregular knee joint including failure mode, strength and stiffness degradation, deformation capacity, bond-slip of reinforcement, and energy dissipation capacity through four large-scale static cyclic tests. The test results show that in general the irregular knee joint designed to the current code has low seismic capacity due to poor bond conditions of the reinforcement inside the joint.

Preliminary analytical study on seismic ductility demand of wood diaphragms

A new seismic design methodology is being proposed for floor diaphragms for various types of construction materials including wood diaphragms. The new design methodology introduces a design acceleration to keep diaphragm elastic under design-basis earthquake using a mode superposition method. On top of this elastic design acceleration, a force reduction factor is proposed in the design methodology by considering available diaphragm ductility capacity and possible post-yielding strain hardening. This article presents an analytical study to examine the relationship between the force reduction factor and the ductility demand for the wood diaphragm using nonlinear dynamic time history analyses. The maximum allowable diaphragm design force reduction factor is determined using the analytical results and available wood diaphragm test data. Recommendations are provided for selection of the force reduction factor for the wood diaphragm for the new design methodology.