Sufficient Lateral Stiffness Research Articles

Seismic resilient steel moment connections with top shear tabs and bottom replaceable metallic fuse: Analytical and experimental study

A new seismic resilient steel moment connection with top shear tabs and bottom replaceable metallic fuse is proposed. The shear tabs are realized by a combination of shear angles, with or without shear plates or splice plates, while a buckling-restrained plate (BRP) is employed as the fuse. Both the shear tabs and BRP are placed at a splice location which represents the beam inflection point under gravity load. Analytical models were developed to determine the stiffness, strength, and deformation of the proposed connection, as well as a trilinear moment-rotation relationship at the spliced section. In this way, a coordinated seismic design procedure to achieve structural serviceability and resilience in steel moment frames with the proposed connection was derived based on the equal-stiffness and zero-moment strategies. Cyclic loading tests of full-scale beam-to-column subassemblies equipped with the proposed connection were conducted. Three resilient connections with different shear tabs (bolted/welded shear angles above/below the beam top flanges) were examined and compared with a conventional fully welded connection. The test results validated the concept and confirmed success of the analytical and design methods to ensure sufficient lateral stiffness and concentrate plastic damage into the BRP. Moreover, the resilient connections with bolted or welded shear angles above the beam top flanges exhibited about 11–18% higher moment resistance at 4% drift and 20% more energy dissipation, and thus are recommended over that with welded shear angles beneath the beam top flanges.

Seismic Assessment of Combined Effects of Knee Bracing and Dog-bone Connections in Dual Moment Frame Systems for Tall Steel Structures

The growing population and urbanization have led to an increasing interest in constructing tall buildings, particularly in large cities. However, the frequent occurrence of earthquakes worldwide has necessitated the development of systems with high ductility and sufficient lateral stiffness. The special dual system of moment frame with bone connections and knee bracing systems are two examples of such systems. In this study, the seismic behavior of these two systems in combination with tall structures was investigated. Ten, thirteen, and sixteen-story frames with four different combinations of bone joints and knee bracing were analyzed using ETABS software. Linear and nonlinear static (pushover) analyses, as well as linear and nonlinear dynamic (time history) analyses, were conducted. Seismic parameters were then calculated for each case and compared. The results emphasized the importance of considering multiple factors and coefficients when evaluating the seismic performance of structures.

Optimum Shape and Position of Outrigger System for High Rise Building under Earthquake Loading

The advancement of high rise building has been increasing on a large scale. In tall structures shear wall often resisted the lateral load induced by wind and earthquake but as the building height increases the stiffness of the structure reduces. To provide sufficient lateral stiffness of the structure implementation of outrigger system between the shear walls and peripheral columns is often used. The aim of this study is to identify the optimum shape of outrigger belt truss in tall buildings under earthquake load condition. A thirty storey with single belt truss, forty five storeys with two belt trusses and sixty storey with three belt trusses structure was investigated with three different shape outrigger belt truss that is X, V and N. The optimum location by providing single belt truss at 10th story, 15th story and at top story in thirty story building is considered in the analysis. From the analysis a comparative study are made with and without variation of shape of outrigger with belt truss with parameters likes storey displacement and storey drift under earthquake loading and get a optimum position of outrigger belt truss for thirty storey building with single belt trusses placing at different locations.

STUDY ON SEISMIC PERFORMANCE AND COLLAPSE-RESISTANT CAPACITY OF TYPICAL FRAME-CORE TUBE STRUCTURES WITH SINGLE AND DUAL LATERAL-FORCE RESISTING SYSTEM

In the design code system of China, frame-core tube structure should be designed as a dual lateral-force resisting system, and there are strict requirements for the secondary lateral-force resisting system of such structure. In other words, the outer frame of the frame-core tube structure should have sufficient lateral stiffness and strength. However, in the design codes of other countries (e.g., ASCE-7 of the United States), the outer frame of the frame-core tube structure is permitted to only carry the vertical load. Therefore, to compare the seismic performances of the single and dual lateral-force resisting systems of the frame-core tube structure, a dual lateral-force resisting system model was firstly designed following the design codes of China. Subsequently, under the same gravity load (and the same concrete consumption), the single lateral-force resisting system model of the frame-core tube structure was design according to the following procedures:1) the secondary lateral-force resisting system was removed from the dual system, and the shear force adjustment of the frame was ignored; 2) the seismic detailing requirement of the frame was lowered to reduce the sectional size. As a result, the tube beared most of the seismic load, and the frame only resisted the vertical load. The structural responses and component damage of these two systems under SLE (Service Level Earthquake) and MCE (Maximal considered earthquake) were analyzed. Furthermore, the collapse mechanisms of two structures and their collapse-resistances were investigated. Finally, the variation of the shear force and shear distribution of the frame under different levels of earthquake and the corresponding damage of key components were discussed. The research shows that the response of the dual system structure was slightly greater than that of the single system, and their collapse resistant capacities were similar. However, the steel consumption of the single system was less than that of the dual system.

A Deployable Brace Model with Joint Clearance and Strut Eccentricity in Seismic Design

The paper discusses seismic performance of deployable brace member as well as its application in single-story single-bay frame by using finite element method in OpenSees Navigator. Even though deployable structure has wide applications in engineering area, it is almost blank for earthquake (seismic) engineering. A finite element deployable brace model consisting two identical struts and a revolute joint is built in this paper. The model considers joint clearance and initial eccentricity to accord practical situation. Hysteresis analysis has been done on the brace model as well as its application. The results show deployable structure provides sufficient lateral stiffness and ductility. Strut eccentricity is the key factor affecting the capacity of the strut and buckling strength, while joint clearance also has influence on the strut capacity and energy dissipation.

BEHAVIOR OF R/C FRAMES WITH CONCRETE PLATE BONDED INFILLS

A practical, economic and effective as well as occupant friendly seismic strengthening technique had been developed for reinforced concrete (RC) framed buildings lacking sufficient lateral stiffness. In this technique, high strength concrete plates are bonded onto the existing plastered hollow brick infill walls using a thin layer of epoxy mortar in order that infill walls are converted into lateral load resisting shear walls resulting from the composite action of infill wall with the plates bonded onto it. By this way, the building gains sufficient lateral stiffness. To analyze the behavior of RC frames strengthened by the aforementioned technique, results of eight one-third scale, one-bay, one or two storey deficient RC frames tested under reverse-cyclic lateral loading until failure are given in detail. Three different types of plates were used to strengthen the frames. Test results showed that the proposed strengthening technique considerably increased the lateral load capacities as well as the initial stiffness and energy dissipation capacities of the strengthened specimens, for both types of frames. Additionally, present study focuses on the comparison results of one-storey specimens with those of equivalent two-storey specimens to well-understand the behavior of such strengthened frames under lateral load, and infill walls under compressive and shear forces as well as tensile forces.

Seismic testing and numerical analysis of Y‐shaped eccentrically braced frame made of high‐strength steel

SummaryIn eccentrically braced frame made of high‐strength steel (HSS‐EBF), link and brace are made from conventional steel whereas other structural members use high‐strength steel. Using HSS for beams and columns in EBF can reduce steel consumption and increase economic efficiency. In this paper, one shake table test of a 1:2 scaled three‐story Y‐shaped HSS‐EBF (Y‐HSS‐EBF) specimen was carried out to study its seismic behavior underground motions with different peak ground accelerations. The dynamic properties, base shear force, displacement, and strain responses of the specimen were obtained from this test. In addition, the finite element models of two 10‐story Y‐HSS‐EBF buildings and one 10‐story conventional Y‐EBF building were evaluated for seismic effects. Nonlinear pushover and dynamic analyses were conducted to compare their seismic performance and economy. The results indicated that the specimen exhibited sufficient lateral stiffness and safety but suffered some localized damages. During the high seismic intensity earthquakes, the links of the test specimen were in inelastic to dissipate the earthquake energy, whereas other structural members remained in the elastic state. Under the same design conditions, Y‐HSS‐EBF used less steel than that of conventional Y‐EBF, which could reduce the amount of steel used in Y‐HSS‐EBF. The Y‐HSS‐EBF is a safe, dual system with reliable seismic performance.

OPTIMUM OUTRIGGER LOCATION IN OUTRIGGER STRUCTURAL SYSTEM FOR HIGH RISE BUILDING.

In modern tall buildings, lateral loads induced by wind or earthquake are often resisted by a system of coupled shear walls. But when the building increases in height, the stiffness of the structure becomes more important and introduction of outrigger beams between the shear walls and external columns is often used to provide sufficient lateral stiffness to the structure. The outrigger and is commonly used as one of the structural system to effectively control the excessive drift due to lateral load, so that, during small or medium lateral load due to either wind or earthquake load, the risk of structural and non-structural damage can be minimized. For high-rise buildings, particularly in seismic active zone or wind load dominant, this system can be chosen as an appropriate structure. The objective of this thesis is to study the outrigger location optimization and the efficiency of each outrigger when three outriggers are used in the structure. In 40−storey three dimensional models of outrigger and belt truss system are subjected to wind and earthquake load, analyzed and compared to find the lateral displacement reduction related t o the outrigger and belt truss system location.

Investigating the Parameters Influencing the Behavior of Knee Braced Steel Structures

In Knee-Braced Frames (KBF), the brace is connected to the knee element rather than the beam-column joint. For reasons such as having sufficient lateral stiffness despite its adequate ductile behavior, the concentration of damage in the Double Knee-Braced structural elements and also ease of repair and replacement of these elements after an earthquake, this bracing system is preferred over conventional systems. The lateral stiffness of this system is provided by the bracing system and the frame ductility is supplied by the flexural yield or the shear yield of the knee members depending on the knee length. Attempts have been made, in the present study, to investigate the non-linear seismic behavior of Knee-Braced Frame systems for various influencing factors and to formulate the effect(s) of the number of building stories, the length of the knee element and moment of inertia of the bending members on the seismic behavior, the drift of the stories and the failure mode of these systems. Finally, based on the results of the study, some recommendations have been offered for the effective range parameters for the optimal performance of these systems.

Seismic behavior analysis for composite structures of steel frame‐reinforced concrete infill wall

SUMMARYThe composite structure of steel frame–reinforced concrete infill wall (CSRC) combines the advantages of steel frames and reinforced concrete shear walls. Reinforced concrete infill walls increase the lateral stiffness of steel frames and reduce seismic demands on steel frames thus providing opportunities to use partially restrained connections. In order to study seismic behavior and load transfer mechanism of CSRC, a two‐story one‐bay specimen was tested under cyclic loads. With that, the main characters such as, strength, stiffness, ductility, energy dissipation, load distribution, performance of steel frames, partially restrained connections and studs, are analyzed and evaluated. The experimental results show that the structure has adequate strength redundancy and sufficient lateral stiffness. The CSRC system has good ductility and energy dissipation capability. Partially restrained connections could enhance ductility and avoid abrupt decreases in strength and stiffness after the failure of infill walls. The composite interaction is ensured by headed studs, which have failed because of low‐cycle fatigue. Steel frames bear 80%–100% of overturning moments, and the remainder is undertaken by infill walls; steel frames and infill walls resisted 10%–20% and 80%–90% of lateral loads, respectively. Furthermore, relevant design recommendations are presented. Copyright © 2011 John Wiley & Sons, Ltd.

Study of Adding Cover—Plate Used For the Single Diagonal Eccentrically Braced Steel Frames

This paper suggested a new connection protocol, adding cover-plate between shear links and column, which was used to enhance moment and shear carrying capacity of beam, relax the restriction and assure the sufficiency development of plastic deformation of the link, and dissipate more earthquake energy. Considering the scale ratio of 1:3, the experimental data was achieved by a specimen under cyclic loading, which was verified by nonlinear finite element analyses. Results indicated that the new type of eccentrically braced steel frame has enough stiffness and deformation capacity, draws link away from flange of column, and dissipates more earthquake energy. The single diagonal eccentri- cally braced frames adopted adding cover-plate protocol would ensure sufficient lateral stiffness under ordinary circum- stances, including lateral loads due to wind and moderate seismic disturbances, have preferable resisting seismic behavior under rare earthquake, and be so practical and costly that they could be easily applied in the present project. Some factors which affect resisting seismic behavior were the thickness of the connection-plate between beam and column, adding stiffeners, and the decrease in the length of A segment etc.

Resisting Seismic Behavior Study of an Adding Cover-Plate Protocol Used For D-Type Eccentrically Braced Steel Frames

This paper suggests a new connection protocol, adding cover-plate between shear links and column, which was used to enhance moment and shear carrying capacity of beam, relax the restriction and assure the sufficiency development of plastic deformation of the link, and dissipate more earthquake energy. Considering the scale ratio of 1:3, the experimental data was achieved by a specimen under cyclic loading, which was verified by nonlinear finite element analyses. Results indicate that the new type of eccentrically braced steel frame have enough stiffness and deformation capacity, draw link away from flange of column, and dissipate more earthquake energy. The single diagonal eccentrically braced frames adopted adding cover-plate protocol will ensure sufficient lateral stiffness under ordinary circumstances, including lateral loads due to wind and moderate seismic disturbances, have preferable resisting seismic behavior under rare earthquake, and be so practical and costly that it can be easily applied in present project.