- Recent earthquakes demonstrated that the collapse prevention of the structures in case of extremely strong ground motions is still a serious societal concern. One approach is to cap the seismic forces applied to structure by separating the superstructure from the foundation and allowing the superstructure to slide. The forces transmitted to the superstructure are controlled by the friction coefficient of the sliding surface, which can be properly reduced by graphite lubrication. This study aims at evaluating the efficiency of the lubricated sliding system on realistic specimens, taking into account the possible influence of the overturning moment, and the level of synchronization in movement of separated column bases.
Characteristics of Free-Standing Structures
Reducing residual deformation is substantial for buildings to achieve continuing business and prompt recovery after earthquakes. A self-centering frame system with rocking using CFT columns was developed. The proposed frame system effectively reduces the residual deformations of the frame through the restoring forces applied by the PC bars installed in the columns. Double-skinned CFT columns using ultra-high strength steel greatly enlarge the strength and elastic deformation capacities of the columns.
Self-centering frame with rocking using CFT columns made of high strength steel
Conventional buckling braces (CBBs) are the most commonly used steel braces but appear some weaknesses. (1) Large stiffness is provided together with the strength demand which increases the base shear and acceleration in structures; (2) Very limited post-yielding stiffness is provided which increases rapidly the inelastic deformation beyond the brace yielding; (3) Intense local mid-length buckling occurs that leads to unstable energy dissipation and early fracture. This research proposes a new steel brace scenario, named Brace with Intentional Eccentricity (BIE), aiming to overcome the aforementioned deficiencies and improve further the seismic performance”
Development and Experimental Investigation of Brace with Intentional Eccentricity
To achieve quick and objective after-earthquake structural condition assessment, steel slit shear walls with X-shaped links were developed, which function as an indicator of the maximum drift ratio experienced in addition to a hysteresis damper. X-shaped links are adopted as they have a large out-of-plane tilting suitable for visual inspection. The wide link tilts at a small drift and the narrow link tilts at a large drift. By identifying the narrowest link to buckle, the maximum drift ratio experienced can be estimated. This developed system was studied in simulations and experiments.
Dual functional steel plate shear walls with X-shaped links
Minimal-disturbance arm damper (MDAD) has been developed to improve the seismic performance of steel frames by restraining local deformation at bottom flanges of beam ends. The primary objectives of this research are: (1) to investigate the performance of MDAD under bidirectional loading and quantify the effect of out-plane deformation; (2) to improve the plate-column attachment and prevent the slippage of MDAD on the column. The performance of MDAD with modified plate-column attachment is investigated by two sets of bidirectional loading tests: quasi-static cyclic loading tests and dynamic tests with sinusoidal wave input.
Minimal-disturbance arm damper (MDAD) for bidirectional loading
Seismic damage assessment for building structures has received much attention due to a significant demand for quick recovery of functions of cities and communities after large earthquakes. For assisting the current visual-based quick inspection process, our group works on the development of prompt and effective seismic damage monitoring techniques for buildings by utilizing smart sensing, wireless sensor networks, and information processing technologies.
(F-1)Post-earthquake decision-making based on structural health monitoring and aftershock risk analysis
(F-2)Strain-based local damage detection and seismic performance evaluation
(F-3)Development of a damage quantification method with a substructure oscillation apparatus
(F-4)Detection of local damages in steel structures using Piezoelectric sensor
In recent years, a system permitting slipping at column bases is proposed to reduce seismic force of structures subjected to large earthquakes. In the previous researches, the friction coefficient between steel column bases and mortar of foundation is around 0.8 in normal steel structures. However, it was reported that the friction coefficient can be reduced to 0.2 if graphite lubricant is used between steel and mortar. This study evaluates the behavior of free standing structures using graphite lubricant under large earthquakes.
Shaking table test and performance evaluation of Free-Standing Structures
Steel braced frame systems, including conventional buckling braced (CBB) and buckling restrained braced (BRB) frames, have been nowadays widely used as seismic resisting systems. However, the braced frames have inherent weaknesses limiting their seismic capability, such as providing no energy dissipation at small drift levels, and providing extremely small post-yield stiffness which would potentially cause the soft-story problem. This research proposes an innovative design of braces with a novel mechanism, entitled Naturally Buckling Braces (NBBs). The design of NBBs combines the use of high-strength and low-yield steels with an intended initial eccentricity and provides an improved and reliable seismic performance avoiding the weaknesses of the existing types of braced frames.”
Development and Experimental Investigation of Naturally Buckling Steel Braces
Structurally-deficient steel frames needs the increase of the earthquake-resisting capacity. This research develops a tension-only bracing system for resource-saving seismic rehabilitation which satisfies following design requirements: (1) to reduce the tensile stresses at critical sections as bottom flanges near beam-column connections; (2) to increase the initial stiffness and strength of original frames, and energy-dissipation capacity; (3) to install the system without the use of welding and occupy only the upper part of opening to keep visibility.
Development of resource-saving seismic rehabilitation using light steel members
Shear wave propagating through buildings vertically can be extracted by applying seismic interferometry method to floor velocity responses under ambient vibration. The wave velocity estimated using two sensors at different floors depends on stiffness of stories between the sensors, from which the damage state of the stories suffered from earthquakes can be evaluated.
Building Damage Detection Using Wave Slowness Changes
H-SA700 steel is a new ultra-high strength steel, which achieves very high strength without introducing intensive heat treatment. The target of this research is to develop a new steel structural system that enables continuous use after major earthquakes. The structural system is achieved by connecting columns, beams, and dampers using only bolts, so that all the components can be replaced, reused, and recycled. The columns are provided with sufficiently large strength to keep them elastic under very rare earthquake events.
Development of building structures using ultra-high strength steel
Various repair and strengthening methods have been developed and proposed for the rehabilitation of damaged steel beam-to-column connections during severe earthquakes. A new method using SFRCC is proposed for the repair of such damaged connections. In the proposed method, steel plates are used to replace the fractured and buckled bottom flanges, and SFRCC slab is used to replace the damaged RC floor slab portion in the vicinity of the column. The experimental study shows that the repaired connection can develop a strength not smaller than the original connection, and the SFRCC slab has nearly no damage even up to 3% drift ratio.
Seismic repair method for steel beam-to-column connection using SFRCC
To apply a steel shear wall technology to seismic retrofit of mid-rise buildings, “slitted steel shear walls restrained by wooden panels” are developed, which are characterized by light weight, low price, and good workability. The shear walls are designed to be installed between openings (e.g., door and window). To ensure the practical use of the new shear walls, a study was carried out on the selection of the thickness of wooden panels and numbers of bolts needed, and the establishment of the design methodology for the proposed slitted steel shear walls.
Slitted steel shear walls restrained by wooden panels
A semi-active controlled floor isolation system is developed to protect a group of valuable equipment free from damage in an earthquake event. To ensure that the semi-active control works effectively under different types of excitations featuring with different frequency characteristics, an LQR control with scheduled gain algorithm is developed. A series of shaking table tests have been conducted and the test results show that semi-active control is more advantageous over the passive control and the semi-active control with the traditional LQR algorithm.
Semi-active controlled floor isolation system with new control algorithm