Adequate Lateral Stiffness Research Articles

Dynamic model, performance analysis and evaluation of frame-distributed rocking-core tube structure

To obtain adequate lateral stiffness for frame-core tube (FCT) structures, the core tube area proportion is often increased and/or overly reinforced which often limits the layout flexibility and economy of the structure. A new high-rise configuration named frame-distributed-core tube (FDCT) is proposed to reduce the tube area proportion of the FCT structure. Combined with a rocking system, the frame-distributed rocking-core tube (FDRCT) structure is further proposed, which aims to reduce the damage caused by soft-stories due to by the weakening of the stiffness of the FDCT structure. Simplified models are built, and the structural dynamics are derived based on the Lagrangian equation. Through numerical simulation of three structures under ground motions, it is shown that the FDRCT structure has good energy dissipation and damping performance. The inter-story drift ratios of the structure decreases with the increase of the distributed rocking tubes mass. Under different site conditions and long-period ground motions, numerical simulations and shaking table tests show that the distributed rocking tubes can effectively reduce the structural response and improve the seismic performance. The FDRCT configuration gives better damping performance under long-period ground motions. A performance-profit evaluation shows that the proposed high-rise structure system of FDRCT provides a safe and cost-effective design solution.

Comparative study of different steel‐concrete composite shear walls

AbstractHigh‐rise buildings are typically subjected to horizontal loads as wind and earthquake, therefore, to provide an adequate lateral stiffness and resistance, structural cores should be considered within the structure.For this reason, to provide alternative yet advantageous solutions, a comparison between concrete cores and composite cores for high‐rise buildings' performances is presented here. Some recent applications in US and China, indeed, showed how the steel‐concrete composite shear wall solution could give better results in terms of construction time and constructability ensuring a significant financial gain.Different ideas of composite shear walls will be presented and parameters of stiffness and resistance for each cross section will be evaluated. Thereafter, the best solutions, in terms of the abovementioned parameters and constructability, will be implemented into a real case of a building, modelled on ETABS software and compared with the original solution in reinforced concrete. In addition to highlighting the structural benefits of the proposed solution, it will be shown that the proposed solution has lower carbon footprint compared to other conventional solutions.

Experimental study on PSPC beam – Concrete encased CFST column frame installed with novel steel panel dampers

A concrete-filled steel tubular (CFST) column has a bearing capacity with a relatively small cross section. From the perspective of the assembly, a partially steel-reinforced precast concrete (PSPC) beam can combine the merits of both the reinforced concrete beam and steel beam. However, strong earthquake action puts forwards a dramatic seismic requirement for the high-rise frame. In this study, to improve the seismic performance of the structure in an economical way, the duplex assembled I-shaped steel panel damper (DAISPD) was introduced to the PSPC beam-concrete encased CFST column frame through the eccentric brace. A half-scaled two-storey two-bay substructure specimen was tested under cyclic loading. A series of seismic properties was then analysed, including the failure modes, hysteretic performance, and energy dissipation capacity. To further investigate the contribution of the damper, groups of numerical analyses were conducted on the key design parameters of the DAISPD. The introduction of the damper provides an adequate lateral stiffness and energy absorption to the frame, especially when the interstorey drift is within the elastic and plastic drift limits. The damage of the damper and the beam hinge mechanism occurs sequentially, which results in a two-stage failure mode. Considering the predamage contribution and the postdamage influence of the damper, it is recommended to design with a moderate yield force and a small height.

Numerical Study on An Innovative Elastomeric‐Steel Cushion Damper

AbstractIn this research cyclic performance of a newly developed energy dissipating device is investigated through finite element studies. The device is constructed using yielding steel Cushions and bonded rubber cubes. The Cushions dissipate the induced energy of earthquakes while the rubber cubes provide lateral constraint and post‐elastic stiffness for the bracing system due to the Hyperelastic behavior of the rubber material. The main advantage of the proposed damper is its little maintenance expense and cost efficiency since the steel Cushions can easily be replaced. In this paper, the requisite details are presented for the application of the proposed device. It can be observed from the analytical results that the proposed damper exhibits full and wide hysteresis loops resulting in excellent equivalent viscous damping while maintaining adequate lateral stiffness at various displacement levels. The dissipated energy per cycle and the respective effective stiffness and equivalent damping of the model are presented in this study.

The influence of the axial restraint on the overstrength of short links

Eccentrically braced frames (EBFs) constitute a good structural solution located between Moment Resisting Frames (MRFs) and Concentrically Braced Frames (CBFs) because they exhibit an adequate lateral stiffness joined with a high ductility capacity, especially for what concerns short and very short links. Link design plays an important role in the effective dissipation capacity of the structure that is well designed only if the link members are involved in plastic range while the other members remain elastic. A proper design of the non-dissipative members needs to account for the link overstrength that results to be very high, especially for very short links.In this paper, the influence of the axial restraints on the evaluation of the link overstrength and ultimate rotation is investigated. A wide parametric analysis is carried out based on a set of shapes selected in the European Standards. FEM simulations are used to develop the parametric analysis after a calibration carried out on experimental tests selected from a literature review. Empirical formulations are also proposed with the scope of providing a more accurate evaluation of the overstrength factor for short and very short links in the framework of EU “I shaped” standard profiles.

Vibration Analysis of EMS-Type Maglev Vehicles Traveling over a Long-Span Bridge with Double Lines

This paper establishes a detailed three-dimensional (3D) model to study the spatial vibration characteristics of two middle-low speed vehicles traveling along a long-span bridge with double lines. Here, two state-space equations for the left- and right-hand maglev vehicles are derived, considering the equations of motion of vehicles, governing equations of currents, linear feedback controls and state observers. By employing the conventional finite element method, the equation of motion for the variable cross-section continuous girder bridge with three spans is simulated. To solve these three coupled equations, this study adopted a new separated iterative approach based on the precise integration method and the Newmark-β method. The total virtual work conducted by the inertial loads, damping loads, elastic loads and fluctuating electromagnetic loads are calculated to conveniently assemble the global mass matrix, damping matrix, stiffness matrix and coefficient matrices of fluctuating electromagnetic forces in the maglev vehicles. The numerical studies indicate that the vertical interactions play dominant roles in the 3D maglev vehicles-bridge system, and the passing maglev vehicles on the bridge have little influence on the lateral motions of the vehicle on the other line due to the adequate lateral stiffness of the bridge.

Effective Shape of RC Frame Building with their Optimum Location of Shear Wall

As per the previous records of earthquakes, there is an increase in the demand of use of earthquake resisting structures. So it is necessary and prime concern of designer to design and analyses the structures by considering seismic effect to provide adequate safety to structure against lateral loads. Many existing RC frame buildings located in seismic zones are deficient to withstand earthquakes. Insufficient lateral resistances, improper shape and poor detailing of reinforcement are the main reasons for inadequate seismic performance of multi-storey building. Shear wall system is one of the most commonly used lateral-load resisting technique for high-rise buildings. Shear walls have very high in-plane strength and stiffness, which can be used simultaneously for resisting large horizontal and gravity loads. In tall buildings, it is very important to ensure adequate lateral stiffness to resist lateral load. The aim of this work is to determine the most effective shape of building with their optimum location of shear wall in multi-storey buildings. For this purpose five different shaped (i.e. square shape, rectangular shape, T-shape, U-shape and H-shape) fifteen storeyed building models each has been with their optimum location of shear wall. Building plan area and shear wall area are same for all different shaped fifteen storeyed building models. Models are analyzed in earthquake zone IV for comparing storey displacement, storey drift, storey shear and time period of buildings. Earthquake load is calculated as per IS: 1893-2016 (Part-1), the various parameters like response reduction factor, importance factor, zone factor are taken from IS: 1893-2016 (Part-1) and are applied to the buildings located in Zone IV. The buildings are modeled and analyzed using software ETAB 2017 and finally concluded that the square shaped building with their optimum location of shear wall is more effective other than different shaped buildings to control the lateral displacement in up to 15 stories buildings.

Effects of Interior Partition Walls on Natural Period of High Rise Buildings

In regions of low to moderate seismicity, serviceability limits states such as inter-story drift under wind load govern the design of the lateral load resisting structural systems of high rise buildings. The key objective in this regard is to provide adequate lateral stiffness to control lateral deflections and inter-story drifts. Current design practice assumes that the structural system alone provides lateral resistance against wind, the dominant load considered for countries like Australia. The contribution of nonstructural components (NSCs) such as interior partition walls on lateral stiffness is generally disregarded in the analysis of the buildings, even though it is commonly acknowledged that the NSCs play a significant role on the lateral stiffness of buildings. This technical note presents the results of a parametric study on the effects of NSCs, in particular, the effects of masonry interior partition walls on the fundamental period of buildings. The parameters considered in this study include: the number and length of walls, their material properties, the number of parallel moment resisting frames and the height of buildings. The results of this study indicate that interior walls can have significant effects on the lateral stiffness of buildings.

Evaluating the ductility characteristics of self-centering buckling-restrained shape memory alloy braces

Recently, self-centering earthquake resistant systems have attracted attention because of their promising potential in controlling the residual drifts and reducing repair costs after earthquake events. Considerable portion of self-centering research is based on using short-segment superelastic shape memory alloy (SMA) braces as strengthening technique because of the lower modulus of elasticity of SMA in comparison with that of steel. The goal of this study is to investigate the ductility characteristics of these newly proposed short-segment SMA braces to evaluate their safety levels against fracture failures under earthquake loading. This goal has been achieved by selecting an appropriate seismic performance criterion for steel frames equipped with SMA braces, defining the level of strain capacity of SMA and calculating the strain demands in the SMA braces by conducting a series of pushover and earthquake time history analyzes on typical frame structure. The results obtained in this study indicated the inability of short-segment SMA designs to provide adequate ductility to the lateral resistant systems. An alternative approach is introduced by using hybrid steel-SMA braces that are capable of controlling the residual drifts and providing the structure with adequate lateral stiffness.

Experimental and numerical study on innovative seismic T-Resisting Frame (TRF)

In common structural systems, there are some limitations to provide adequate lateral stiffness, high ductility, and architectural openings simultaneously. Consequently, the concept of T-Resisting Frame (TRF) has been introduced to improve the performance of structures. In this study, Configuration of TRF is a Vertical I-shaped Plate Girder (V.P.G) which is placed in the middle of the span and connected to side columns by two Horizontal Plate Girders (H.P.Gs) at each story level. System performance is improved by utilizing rigid connections in link beams (H.P.Gs). Plastic deformation leads to tension field action in H.P.Gs and causes energy dissipation in TRF; therefore, V.P.G. High plastic deformation in web of TRF\'s members affects the ductility of system. Moreover, in order to prevent shear buckling in web of TRF\'s members and improve overall performance of the system, appropriate criteria for placement of web stiffeners are presented in this study. In addition, an experimental study is conducted by applying cyclic loading and using finite element models. As a result, hysteresis curves indicate adequate lateral stiffness, stable hysteretic behavior, and high ductility factor of 6.73.

Seismic Response of Flexibily-Connected Steel Frames

The response of typical low-rise steel building frames designed by the 2 Consctruction method to moderate earthquakes is examined. Such frames are often identified by large girders, small columns, and semi-rigid connections. The simple methods underlying the Type 2 design approach do not permit realistic consideration of the frame response to either static or dynamic loads. In this paper, typical flexibly connected Type 2 fiames will be analyzed for seismic resistance with the methods recommended by the 1988 Uniform Building Code. The results indicate that these Type 2 frame possess adequate strength, but may not have adequate lateral stiffness for moderate seismic loads

Review of Techniques for Predicting the Fundamental Period of Multi-Storey Buildings: Effects of Nonstructural Components

The design of lateral load resisting elements of tall buildings in regions of low to moderate seismicity is normally governed by the requirements to meet inter-storey drift limit under wind load. The key objective of the design of tall buildings is to provide adequate lateral stiffness to the buildings to limit their lateral deflections and inter-storey drifts under the lateral load. The current design practice assumes that only the structural skeleton provides lateral resistance against wind load. Although the effects of nonstructural elements on the lateral stiffness are widely acknowledged, the effects are often ignored in the analysis of the buildings. This paper presents a state-of-the-art of review on the effects of nonstructural elements on the lateral deflections and inter-storey drifts of buildings at serviceability limit states. It was found that ignoring the nonstructural elements could significantly underestimate the lateral deflection for certain types of buildings. However, the shape and form of the lateral deflection in the overall building is not significantly affected by the nonstructural elements.

Seismic Response of Flexibily-Connected Steel Frames

The response of typical low-rise steel building frames designed by the "Type 2 Consctruction" method to moderate earthquakes is examined. Such frames are often identified by large girders, small columns, and semi-rigid connections. The simple methods underlying the Type 2 design approach do not permit realistic consideration of the frame response to either static or dynamic loads. In this paper, typical flexibly connected Type 2 fiames will be analyzed for seismic resistance with the methods recommended by the 1988 Uniform Building Code. The results indicate that these Type 2 frame possess adequate strength, but may not have adequate lateral stiffness for moderate seismic loads

Frames with Staggered Panels: Experimental Study

A structural system consisting of story-deep and bay-wide discrete panels to resist lateral loads is investigated. To study the overall behavior of this system and to compare with the conventional shear wall frame, four perspex models were tested for static as well as dynamic response. To investigate the behavior of a discrete shear panel and to study the effect of stress-concentration at panel-corners where skeletal members meet, three reinforced concrete panels were tested. The proposed system is found to provide adequate lateral stiffness to resist horizontal loads such as wind and earthquake forces. Discrete panels cannot be idealized as line elements (wide columns with rigid arms), and the finite element method must be used for the analysis of staggered panel frames. Local failure at corners of a panel can be avoided by extending the girder and column reinforcements through the length and height of the panel. Reinforcement in the interior of a panel can be the minimum required to resist the stresses due to shrinkage, temperature, and creep.

Light Gage Steel Infill Panels in Multistory Steel Frames

In the design of multistory structures, providing adequate lateral stiffness is often more difficult than satisfying strength requirements. For steel structures of 20 or more stories, deep or heavy beams are often required to maintain drift within acceptable limits. In many structures, vertical trusses, concrete shear walls, or a combination of these and rigid frames are used to achieve the required displacements. For very tall structures, various types of tube construction are often used. The price paid for achieving stiffness in these ways is a decrease in the ductility of the structure, with important effects on its behavior under earthquake loading. The reason for this is that the increased total lateral base shear, required for stiffer systems by the Uniform Building Code, sometimes results in a change to a less ductile system. It is desirable to achieve an increase in stiffness without paying the penalty in decreased ductility. One attempt to do this is the slit concrete panel construction which the Japanese have developed. Normally, the strength and stiffness of infilling elements such as interior and exterior partitions are ignored in designing multistory frames, although such elements are acknowledged to make a substantial contribution to the lateral stiffness of the structure. A research program sponsored by the Committee of Structural Steel Producers and the Committee of Steel Plate Producers of the American Iron and Steel Institute was begun at Cornell University to assess the suitability of light gage steel infill panels for providing additional stiffness in multistory structures. The first portion of the research focused on developing the capability to analyze the infill-frame combination, making use of the finite element displacement method of analysis. The second portion, which is currently in progress, is an attempt to verify the analytical results experimentally and to assess the behavior of the panel-frame combinations at loads for which elastic analysis is not valid.