• Earthquakes and Structures
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• 제11권4호
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• pp.665-680
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• 2016

This paper focuses on the study of seismic behavior of steel reinforced concrete special-shaped column-beam joints. Six specimens, which are designed according to the principle of strong-member and weak-joint core, are tested under low cyclic reversed load. Key parameters include the steel form in column section and the ratio of column limb height to thickness. The failure mode, load-displacement curves, ductility, stiffness degradations, energy dissipation capacity and shear deformation of joint core of the test subassemblies are analyzed. The results indicate that SRC special-shaped column-beam joints have good seismic behavior. All specimens failed due to the shear failure of the joint core, and the failure degree between the two sides of joint core is similar for the exterior joint but different for the corner joint. Compared to the joints with channel steel truss, the joints with solid web steel skeleton illustrate better ductility and energy dissipation capacity, but the loading capacity and stiffness are roughly close. With the increasing of the ratio of column limb height to thickness, the joints illustrate higher loading capacity and stiffness, better energy dissipation capacity, but worse ductility.

• Earthquakes and Structures
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• 제12권2호
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• pp.201-211
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• 2017

This paper experimentally investigates the effect of yield strength of reinforcing bars and stirrups on the seismic performance of reinforced concrete (RC) circular piers. Reversed cyclic loading tests of nine-large scale specimens with longitudinal and transverse reinforcement of different yield strengths (varying between HRB335, HRB500E and HRB600 rebars) were conducted. The test parameters include the yield strength and amount of longitudinal and transverse reinforcement. The results indicate that the adoption of high-strength steel (HSS) reinforcement HRB500E and HRB600 (to replace HRB335) as longitudinal bars without reducing the steel area (i.e., equal volume replacement) is found to increase the moment resistance (as expected) and the total deformation capacity while reducing the residual displacement, ductility and energy dissipation capacity to some extent. Higher strength stirrups enhance the ductility and energy dissipation capacity of RC bridge piers. While the product of steel yield strength and reinforcement ratio ($f_y{\rho}_s$) is kept constant (i.e., equal strength replacement), the piers with higher yield strength longitudinal bars are found to achieve as good seismic performance as when lower strength bars are used. When higher yield strength transverse reinforcement is to be used to maintain equal strength, reducing bar diameter is found to be a better approach than increasing the tie spacing.

• Earthquakes and Structures
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• 제14권3호
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• pp.261-271
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• 2018

Fiber reinforced cementitious composites (FRCC) materials that exhibit strain-hardening and multiple cracking properties under tension were recently developed as innovative building materials for construction. This study aims at exploring the use of FRCC on the seismic performance of coupling beams with conventional reinforcement. Experimental tests were conducted on seven FRCC precast coupling beams with small span-to-depth ratios and one ordinary concrete coupling beam for comparison. The crack and failure modes of the specimens under the low cycle reversed loading were observed, and the hysteretic characteristics, deformation capacity, energy dissipation capacity and stiffness degradation were also investigated. The results show that the FRCC coupling beams have good ductility and energy dissipation capacities compared with the ordinary concrete coupling beam. As the confinement stirrups and span-to-depth ratio increase, the deformation capacity and energy dissipation capacity of coupling beams can be improved significantly. Finally, based on the experimental analysis and shear mechanism, a formula for the shear capacity of the coupling beams with small span-to-depth ratios was also presented, and the calculated results agreed well with the experimental results.

• Steel and Composite Structures
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• 제25권5호
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• pp.603-615
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• 2017

This experimental research presents the seismic performance of steel reinforced high-strength concrete (SRHC) short columns. Eleven SRHC column specimens were tested under simulated earthquake loading conditions, including six short column specimens and five normal column specimens. The parameters studied included the axial load level, stirrup details and shear span ratio. The failure modes, critical region length, energy dissipation capacity and deformation capacity, stiffness and strength degradation and shear displacement of SRHC short columns were analyzed in detail. The effects of the parameters on seismic performance were discussed. The test results showed that SRHC short columns exhibited shear-flexure failure characteristics. The critical region length of SRHC short columns could be taken as the whole column height, regardless of axial load level. In comparison to SRHC normal columns, SRHC short columns had weaker energy dissipation capacity and deformation capacity, and experienced faster stiffness degradation and strength degradation. The decrease in energy dissipation and deformation capacity due to the decreasing shear span ratio was more serious when the axial load level was higher. However, SRHC short columns confined by multiple stirrups might possess good seismic behavior with enough deformation capacity (ultimate drift ratio ${\geq}2.5%$), even though a relative large axial load ratio (= 0.38) and relative small structural steel ratio (= 3.58%) were used, and were suitable to be used in tall buildings in earthquake regions.

• Structural Engineering and Mechanics
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• 제64권3호
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• pp.301-310
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• 2017

For further development of passive control systems to dissipate larger seismic energy and prevent the structures from earthquake losses, this paper proposes an innovative two-level control system to improve behavior of chevron braced steel frames. Combining two Knee Braces, KB, and a Vertical Link Beam, VLB, in a chevron braced frame, this system can reliably sustain main shock and aftershocks in steel structures. The performance of this two-level system is examined through a finite element analysis and quasi-static cyclic loading test. The cyclic performances of VLB and KBs alone in chevron braced frames are compared with that of the presented two-level control system. The results show appropriate performance of the proposed system in terms of ductility and energy dissipation in two different excitation levels. The maximum load capacity of the presented system is about 30% and 17% higher than those of the chevron braced frames with KB and VLB alone, respectively. In addition, the maximum energy dissipation of the proposed system is about 78% and 150% higher than those of chevron braced frames with VLB and KB respectively under two separate levels of lateral forces caused by different probable seismic excitations. Finally, high performance under different earthquake levels with competitive cost and quick installation work for the control system can be found as main advantages of the presented system.

• Earthquakes and Structures
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• 제19권5호
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• pp.361-377
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• 2020

In the present research work, the effectiveness and the efficiency of a retrofitting approach using a layer of ultra-high performance fiber reinforced concrete (UHPFRC) jacket for damaged substandard exterior beam-column joints (BCJs) is experimentally investigated. The main objective of this study is to rehabilitate the already damaged BCJs to meet the serviceability requirements without compromising safety. According to the proposed strengthening technique, a chipped surface, lightly brushed with a dry condition was selected for making a successful bond between normal concrete substrate surface (NCSS) and UHPFRC. Then a fresh UHPFRC jacket with a thickness of 30 mm was cast around the damaged specimens. The entire test matrix was comprised of three 1/3 scale damaged exterior BCJs with a different column axial load (CAL). These specimens were repaired with UHPFRC and retested under monotonic loading. Based on the experimental results, repaired specimens showed an excellent performance in terms of their load-displacement response, maximum strength, displacement ductility, initial stiffness, secant stiffness and energy dissipation capacity when compared with the corresponding values registered when these specimens were tested in their virgin state. This rehabilitative intervention not only restored the strength, stiffness, ductility and energy dissipation capacity of severely damaged specimens but also improved their performance.

• Structural Engineering and Mechanics
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• 제61권4호
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• pp.483-496
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• 2017

Earthquake excitations may induce important amount of seismic energy into structures. Current design philosophy mainly deals with the plastic deformations of replaceable energy dissipating devices rather than damages accumulated on structural members. Since earthquake damage is substantially concentrated on these devices they could be replaced after severe earthquakes. In this study, the efficiency of steel cushion (SC) on seismic improvement of a vulnerable reinforced concrete (RC) frame is determined by means of several numerical simulations. The cyclic shear behaviors of SCs were determined by performing quasi-static tests. The test results were the main basis of the theoretical model of SCs which were used in the numerical analysis. These analyses were performed on three types of RC frames namely bare frame (BF), full-braced frame (F-BF) and semi-braced frame (S-BF). According to analysis results; implementation of SCs has considerable effects in reducing the storey shear forces and storey drifts. Moreover plastic energy demands of structural elements were reduced which indicates a significant improvement in seismic behavior of the RC frame preventing damage accumulation on structural elements. Full-braced frame having SCs with the thickness of 25 mm has better performance than semi-braced frame interms of energy dissipation. However, global energy dissipation demand of S-BF and F-BF having SCs with the thickness of 18 mm are almost similar.

• 오토저널
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• 제2권1호
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• pp.39-50
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• 1980

This paper presents the variations obtained in heat flow rate and engine performance of a four-stroke cycle Diesel engine when there were changes in the temperature of cooling water, compression ratio, injection timing of fuel, and other factors. Heat dissipation of engine cylinder was calculated by the heat transfer coefficient of Nusselt's empirical equation and the analysis of distribution of temperature in cylinder barrel was obtained by the finite element method of two-dimensional steady state heat conduction. In this experiment, the out side temperature of cylinder liner was measured by the data logger, and the temperature distribution of liner was computed by the analysis of triangular finite element model under the assumption due to surface heat flux of cylinder inner surface. The results obtained by this study are as follows. Under the given operating condition, the temperature distribution of cylinder liner by using finite element method shows that the mean temperature of barrel is in accordance with the experimental results of Eichelberg and temperature difference is lower than 4.23.deg. C. The heat dissipation of engine decrease in accordance with the decrease of piston mean velocity, compression ratio, and the increase of coolant temperature. Influence on the delay of injection timing of fuel brings about the decrease of heat rejection over the cylinder at constant test conditions.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.715-719
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• 2009

In this study, a method to predict the consolidation behavior of soft clays and marine clays was developed by combining the equation of Terzaghi's 1-dimensional consolidation and CPTu dissipation. The special attention was given to the consolidation anisotropy due to the difference between 1-D consolidation and radial consolidation of CPTu dissipation. The analysis combining two equations enables direct application of CPTu results. And above all it doesn't require to sample undisturbed specimens and determine consolidation coefficient which is both costly and time consuming and often contains measuring error. It is also advantageous that CPTu test can be carried out any position and any depth. Clays typically have a greater horizontal permeability, $k_h$, than vertical permeability, $k_v$, and the coefficient of consolidation in the horizontal direction is generally higher than the vertical direction. Various data of horizontal and vertical consolidation coefficient ratio were collected and analyzed to develop and verify the method.

• Structural Engineering and Mechanics
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• 제29권2호
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• pp.187-201
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• 2008

Earthquake induced hysteretic energy demand for a structure can be used as a limiting value of a certain performance level in seismic design of structures. In cases where it is larger than the hysteretic energy dissipation capacity of the structure, failure will occur. To be able to select the limiting value of hysteretic energy for a particular earthquake hazard level, it is required to define the variation of hysteretic energy in terms of probabilistic terms. This study focuses on the probabilistic evaluation of earthquake induced worst failure probability and approximate confidence intervals for inelastic single-degree-of-freedom (SDOF) systems with a typical steel moment connection based on hysteretic energy. For this purpose, hysteretic energy demand is predicted for a set of SDOF systems subject to an ensemble of moderate and severe EQGMs, while the hysteretic energy dissipation capacity is evaluated through the previously published cyclic test data on full-scale steel beam-to-column connections. The failure probability corresponding to the worst possible case is determined based on the hysteretic energy demand and dissipation capacity. The results show that as the capacity to demand ratio increases, the failure probability decreases dramatically. If this ratio is too small, then the failure is inevitable.