Steel Structures Research Update: Self-Centering Column Base Connections with Friction Dampers

SUMMARYThe influence of residual interstorey drifts on economic losses in building resulting from earthquakes is examined. Current building‐specific loss estimation methodologies that estimate economic losses based on peak response quantities such as peak interstorey drift ratios or peak floor accelerations are extended to explicitly account for residual interstorey drifts. The new approach incorporates the influence of residual drifts by accounting for the possibility of having to demolish a building as a result of excessive residual interstorey drifts, where the probability of demolition is computed as a function of the maximum residual drift in the building. The proposed approach is illustrated by estimating direct economic seismic losses in four reinforced concrete moment‐resisting frame buildings in Los Angeles, California. Two buildings have nonductile detailing representative of pre‐1970s building codes, whereas the other two buildings have ductile requirements satisfying current seismic building codes in the U.S. Results indicate that economic losses at intermediate levels of ground motion intensity are often dominated by losses due to residual interstorey drifts. This is particularly true in the case of ductile buildings in which neglecting losses from residual drifts can lead to significant underestimations of economic losses. Copyright © 2012 John Wiley & Sons, Ltd.

A novel double slip loads friction damper to control the seismic response of structures

Earthquakes can be catastrophic phenomena that cause casualties, injuries, and significant damage to buildings.The damage magnitude to individuals and assets caused by earthquakes is mostly determined by the performances of buildings to withstand seismic forces.The current study investigates the performance of friction damper under different earthquake loads considering different configuration using three-dimensional finite element software ETABS.The friction damper was represented by Bouc-Wen model and location optimization was studied.The investigation was carried out to explore the impact of damper optimum placement and configuration.The result showed that using the friction damper in the ten-story building reduced both maximum displacement and the maximum acceleration occurs during the earthquakes events.Also, the result showed the behavior of the diagonal, chevron and the upper toggle friction damper as the location of the damper change across the stories.Finally, the results demonstrate that upper toggle friction dampers significantly reduce seismicinduced displacements and accelerations include up to a 36% reduction in overall displacements and a 35% reduction in peak accelerations compared to undamped structures.Additionally, using a diagonal friction damper (DFD) resulted in a maximum displacement reduction (MTDR) of 30% and a maximum acceleration of 18%.Furthermore, the implementation of a chevron friction damper led to a 29% decrease in maximum displacement and an 23% increase in maximum acceleration.

ABSTRACTA FREE from DAMage friction connection is a connection where friction dampers are introduced by adding friction pads, sliding on slotted steel plates, pre‐stressed with high strength bolts. Even though such a technology provides great advantages in terms of removal of damage to the structural elements, it has the main drawback to provide a limited re‐centering capability. In fact, during a seismic loading history, FREEDAM joints rotate concentrating the dissipation in the friction interface but, due to their high stiffness, after the end of the ground motion, they remain in a deformed position, leaving also the structure with residual drifts resulting in out‐of‐plumbs.The goal of the work is to propose an approach to provide FREEDAM structures with a self‐centering capacity by studying particular devices, to be installed in beam‐to‐column joints or column base joints. In this paper, the attention is focused on the problem of re‐centering of base plate joints studying a detail consisting in a connection located at the base of the columns of the first storey equipped with friction dampers and threaded bars. The threaded bars work as elastic springs thanks to sets of Belleville washers used to increase the deformability and to allow the opening of a gap in the connection. The main breakthrough of the proposed technology with respect to the existing literature, aside from the methodology employed for the design of the friction connection, is that the self‐centering capability is obtained with re‐centering elements (threaded bars and Belleville springs) which are not conceived to be extended up to the end of the column at the top storey of the building, but they have a size similar to the column splice's cover plates. The work reports the results of a preliminary experimental investigation on this joint detail which has regarded cyclic and pseudo‐dynamic tests. The experimental results presented seems very encouraging towards the possible development of base plate joints with self‐centering capacity combined with friction dampers.

Aiming to isolate disturbance vibration for heavy machines with low frequency, a novel hydro-pneumatic vibration isolator with high-static and low-dynamic (HSLD) stiffness is proposed, which contains bellows structure as elastic element and pressurized gas and incompressible liquid as working media. Due to that the natural frequency of isolation system with such isolator is close to zero and loading capacity can be adjusted by the gas pressure, the proposed device is termed as pneumatic near-zero frequency (NZF) vibration isolator. To obtain the mathematical model of isolator’s stiffness, the quasi-static derivation based on gas state equation is carried out first. Results prove that the presented isolator possesses ideal high-static and low-dynamic stiffness, which is also verified by the experimental data measured by a quasi-static test. The proportion of gas volume to total volume of gas and liquid media, respectively, in bellows and cylinder chambers are significant physical parameters, which dominate the nonlinearity extent of isolator’s stiffness. Different from most existing isolators, the proposed isolator includes fluidic damping and friction damping. The former is expressed by classic square-velocity-type nonlinear model, and the latter is modeled as Coulomb damping. To obtain dynamic response and vibration isolation transmissibility, the harmonic balance method is applied. A direct current term is added in the trial solution, which reflects the asymmetry of dynamic response. In respect of transmissibility analysis, square-velocity nonlinear damping brings a favorable advantage that it can ensure the fine force transmissibility in both resonance region and effective isolation band. This conclusion holds consistently under base motion excitation. Friction damping cannot give the same conclusion. Further comparison with a linear vibration isolator exhibits that the HSLD stiffness characteristics of the NZF isolator breaks through the trade-off between large loading capacity and small static deformation, and the square nonlinearity of fluid damping is able to overcome the dilemma that weak linear vicious damping is beneficial for isolation performance within the effective isolation frequency band, but cannot suppress resonance amplitude and transmissibility. And the experimental transmissibility is in good agreement with the analytical result. Besides, the influences of excitation variation on isolation performance are estimated theoretically. Due to the hardening stiffness, overload acceleration will cause the increase in linearized natural frequency of NZF isolator system, and thus, isolation effectiveness will be reduced.

Several experimental lap shear tests have been performed to assess the initial values of the slip resistance and their evolution during a cyclic loading history. Both friction dampers with parallel slotted holes and double slotted holes have been investigated. Friction devices with shims made of a previously tested material, called M4, have been tested and the tribological behaviour, the degradation of the friction coefficient, the influence of the bolts’ preload and the effect of Belleville washers have also been investigated. Moreover, a phenomenological model for the force-displacement response has been calibrated for the modelling of the cyclic response of the friction device. This is particularly important for the development of non-linear dynamic analyses of seismic resistant frames equipped with friction joints aiming at an accurate prediction of the structural response during a seismic event. Finally, a quality control of the friction properties of different batches of friction shims has been performed by means of the Fisher-Berens and Snedecor tests.

The sliding hinge joint (SHJ) is a supplemental energy dissipation system for column bases or beam-to-column connections of steel Moment Resisting Frames (MRFs). It is based on the application of symmetric/asymmetric friction dampers to develop a dissipative mechanism alternative to the column/beam yielding. This typology was initially proposed in New Zealand and, more recently, is starting to be tested and applied also in Europe. While on the one hand this technology provides great benefits such as the damage avoidance, on the other hand, due to the high unloading stiffness of the dampers in tension or compression, its cyclic response is typically characterized by a limited self-centering capacity.To address this shortcoming, the objective of the work herein presented is to examine the possibility to add to these connections also a self-centering capacity proposing new layouts based on a combination of friction devices (providing energy dissipation capacity), pre-loaded threaded bars and disk springs (introducing in the joint restoring forces).In this paper, as a part of an ongoing wider experimental activity regarding the behavior of self-centering connections, the attention is focused on the problem of achieving the self-centering of the column bases of MRFs by studying a detail consisting in a column-splice equipped with friction dampers and threaded bars with Belleville disk springs, located above a traditional full-strength column base joint. The main benefits obtained with the proposed layout are that: (i) the self-centering capability is obtained with elements (threaded bars and Belleville springs) which have a size comparable to the overall size of the column-splice cover plates; (ii) all the re-centering elements are moved far from the concrete foundation avoiding any interaction with the footing. The work reports the main results of an experimental investigation and the analysis of a MRF equipped with the proposed column base joints.

Quasi-static cyclic tests on a half-scaled two-storey steel frame equipped with Crescent Shaped Braces

Experimental study on seismic performance of replaceable shear links with low-yield-point steel

Development, testing and performance evaluation of steel beam-through framed connections with curved knee braces for improving seismic performance

In this paper， experimental studies were conducted on the mechanical properties of typical components of a practical prefabricated shear wall structure， including grouting sleeves， laminated reinforced concrete slabs containing joints， and joints between laminated slabs and prefabricated reinforced concrete shear walls. Industrial computerized tomography （CT） and pull-out tests were conducted on the grouting sleeves connecting the vertical rebars of the upper and lower prefabricated shear walls. It was found that the rebars were generally difficult to align in actual construction. However， the pull-out properties of grouting sleeves met the requirements. Static loading tests were conducted on the slabs. Both slab specimens showed good flexural ductility， and their experimental and calculated bearing capacity values were in good agreement. Quasi-static cyclic tests were conducted on the joints. The load-deflection skeleton curves showed an inverted S-shape， indicating good ductility and energy dissipation capacity. The bearing capacities and failure modes of all three types of components met the design requirements.

Design, simulation and test on the shape optimization of a steel shear key (SSK)

Experimental study on the residual seismic performance of CFDST columns after contact explosion

Lateral load behavior of connections in Assam-type wooden houses in the Himalayan region of India

In historic stone masonry buildings, strong ground motions typically result in out-of-plane failure of the walls before their in-plane strength is reached. This phenomenon is especially pronounced in structures characterized by long unsupported spans perpendicular to their plane, in the absence of a diaphragm effect. In such cases, the strengthening intervention for the historic façade should be selected by considering the principles of conservation. The present study investigates the effectiveness of an innovative reinforcing configuration that builds upon the steel-cord-based techniques available in the literature, using experimental and numerical methods. The applied strengthening consists of no-tensioned steel cords embedded in the bed joints and vertically in both the head joints and the stone bricks of the masonry wall. A large-scale stone masonry wall specimen was designed and constructed to reflect the results of on-site material and dynamic tests performed on a reference historic masonry structure. A series of dynamic and quasi-static cyclic tests was conducted on both the unreinforced and reinforced conditions of the specimen. The proposed method was found to restore the out-of-plane strength without significantly increasing the stiffness of the damaged specimen. Furthermore, it was observed to improve the out-of-plane deformation capacity and overall structural integrity. The finite element models were calibrated based on the test data and exhibited a noteworthy agreement with the experimental results, particularly in terms of load–drift response and damage observations. Some model parameters were also proposed.