Bypass Viscous Damper Performance Assessment in 8-story structure | Seismic Behavior in Masonry Cladding

Introduction 

In recent years, many structures have collapsed due to earthquakes. Seismic loads from earthquakes are dynamic forces that induce free vibrations in structures. This results in deflections in all directions, increasing the risk of failure for structural members. While some elements, like dampers, can dissipate earthquake energy, structures in seismic zones require design according to specific seismic loads based on standards. However, there is a lack of guidance for designing structures with dampers, especially novel ones. To address this, extensive experiments and simulations are necessary. By quantifying energy dissipation by dampers and adjusting structural stiffness, we can simulate their performance in steel and reinforced concrete frames. This package evaluates the dynamic behavior of a developed bypass viscous damper, featuring a flexible hose as an external orifice for fluid transfer. We also propose a simplified design procedure for structures incorporating these dampers. An eight-story hospital is designed with and without bypass dampers and compared to a version with concentric braces. Nonlinear time history analyses show that the hospital with viscous dampers experiences reduced structural inelastic demands and story accelerations, leading to lower demands on nonstructural components. Additionally, the seismic performance of nonstructural masonry claddings is compared between the two hospital designs. Moreover, seismic behaviors of nonstructural masonry claddings are also compared in the cases of hospital structures with and without dampers. This project will utilize three distinct methods, each of which will be the subject of a separate workshop.

What is the developed bypass viscous damper?

The developed bypass viscous damper is similar to other viscous dampers except that it has an external high-pressure but flexible hose as the orifice. It is well understood that during dynamic excitations, the input energy would be dissipated into heat, and the temperature of the damper oil, especially inside the orifice, could greatly increase up to 400 ⁰F. Accordingly, thermal compensation is important in viscous dampers, and the external orifice of the bypass viscous damper would act as a thermal compensator to alleviate the viscous heating of the damper. Moreover, the damping coefficient and damping exponent can be adjusted by the length, diameter, and flexibility of the hose, among others. In this package, the dynamic behavior of a developed bypass viscous damper is evaluated. A bypass viscous damper has a flexible hose as an external orifice through which the inside fluid transfers from one side to the other side of the inner piston. Accordingly, the viscosity coefficient of the damper can be adjusted using the geometrical dimensions of the hose. Moreover, the external orifice acts as a thermal compensator and alleviates the viscous heating of the damper.

How can the developed bypass viscous damper be simulated in the CFD and structural models?

To investigate the performance of the proposed viscous damper, the CFD simulation using ABAQUSand experimental tests are utilized. Two numerical approaches, which involved CFD in ABAQUS and a simplified Maxwell model in SAP 2000, are used to evaluate the performance of this viscous damper in a structure. According to experimental results, the CDF model, a numerical formula, and the simplified Maxwell model are found and assessed; therefore, the verification of numerical and computational models is evaluated for simulation. In this package, a simplified procedure is proposed to design structures with bypass viscous dampers. The design procedure is applied to design an 8-story hospital structure with bypass viscous dampers, and it is compared with the same structure, which is designed with concentric braces and without dampers. Nonlinear time history analyses show that the hospital with viscous damper experiences less structural inelastic demands and fewer story accelerations, which means fewer demands on nonstructural elements. Moreover, seismic behaviors of nonstructural masonry claddings are also compared in the cases of hospital structures with and without dampers.

Method 1: Finite volume method (FVM) for bypass viscous damper

CFD models are used to simulate the behavior of the bypass viscous damper. Only the fluid parts of the damper are simulated by using the CFD model in ABAQUS, and the effect of the other solid parts (piston, cylinder, hose walls, etc.) on the turbulent fluid flow is considered by defining no-slip boundary condition at the fluid-solid interface. Different input velocities are imposed on the model and from the obtained pressure difference at the front and the back of the piston, the corresponding damper force can be evaluated. In this way, the force-velocity curve of the damper can be estimated, as mentioned in the experimental results. The results are compared to experimental results for the validation of the CFD model. The simplified design procedure is described in this package, in which a step-by-step simplified design method is presented to design buildings with viscous dampers.

Method 2: Simulation of the developed bypass viscous damper in structural design

In this section, a step-by-step simplified design procedure is proposed for designing buildings with viscous dampers. In order to attain a desired target damping ratio, the required total damping coefficient of linear viscous dampers can be estimated. The designer should decide how to optimally distribute the obtained total damping into different stories. The performance of the viscous dampers is dependent on velocity; therefore, selecting a damper is dependent on the velocity of the story. As a result, the drift of the upper story requires the selection of a placement for a damper. On the other hand, the most suitable stories would be selected to place a viscous damper related to the highest inter-story velocity. According to period elongation due to inelastic behaviors, the stories with the highest inter-story drifts are expected to also experience the highest inter-story velocities. According to the dependence of velocity and inter-story drift, more damping coefficient should be applied in placements in which there is more inter-story drift. Based on the first mode of structure frame analysis, the pattern of inter-story drifts during a seismic event can be estimated. Accordingly, the total damping coefficient is calculated by a proposed equation, which should be distributed for each story based on the inter-story drift value of each story per summation of all inter-story drift. This procedure will be explained in more detail in the subsequent section.

Method 3: The effect of the developed bypass viscous damper on structural behavior and material

The structure of a hospital as a case study is considered to be designed with and without this viscous damper for evaluating the performance of this viscous damper in the specified structure; therefore, two same hospital structures are modeled with and without this viscous damper by using SAP2000, which details this method is described in this package. After analyzing these structures, one of the nonstructural masonry claddings at the 8th story, which is located in the same place in the two structures, is considered to evaluate the performance of the viscous damper on nonstructural masonry claddings; therefore, these walls are modeled and analyzed based on the exported load of SAP models in ABAQUS/Standard.

Workshop 1: Simulation of the performance of the bypass viscous damper by FVM

In this workshop, first, the simulation of the bypass viscous damper using the CDF model is presented. Using this model, an equation is presented that can represent the performance of the bypass viscous damper.

Workshop 2:  Representing the performance of the bypass viscous damper in the structure

In this Workshop, a step-by-step simplified design procedure is proposed for designing buildings with viscous dampers. In order to attain a desired target damping ratio, the required total damping coefficient of linear viscous dampers can be estimated. An approach to specifying the optimal place for the bypass viscous damper is presented to the structural engineer and designer.

Workshop 3:  Reduction of the damage in a structure with the developed bypass viscous damper

The structural behavior of a hospital with and without the developed bypass viscous damper is evaluated and compared. For this target, two similar hospital structures are simulated with and without this viscous damper by using SAP2000, which this simulation in detail is described in this package. After analyzing these structures, one of the nonstructural masonry claddings at the 8th story, which is located in the same place in the two structures, is analyzed to evaluate the performance of the viscous damper on nonstructural masonry claddings that the simulation of masonry claddings is conducted by ABAQUS.