• Structural Engineering and Mechanics
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• v.81 no.6
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• pp.715-728
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• 2022

A new type of buckling-restrained braces (BRBs) with a longitudinally profiled steel plate working as the core (LPBRB) is proposed and experimentally investigated. Different from conventional BRBs with a constant thickness core, both stiffness and strength of the longitudinally profiled steel core along its longitudinal direction can change through itself variable thickness, thus the construction of LPBRB saves material and reduces the processing cost. Four full-scale component tests were conducted under quasi-static cyclic loading to evaluate the seismic performance of LPBRB. Three stiffening methods were used to improve the fatigue performance of LPBRBs, which were bolt-assembled T-shaped stiffening ribs, partly-welded stiffening ribs and stiffening segment without rib. The experimental results showed LPBRB specimens displayed stable hysteretic behavior and satisfactory seismic property. There was no instability or rupture until the axial ductility ratio achieved 11.0. Failure modes included the out-of-plane buckling of the stiffening part outside the restraining member and core plate fatigue fracture around the longitudinally profiled segment. The effect of the stiffening methods on the fatigue performance is discussed. The critical buckling load of longitudinally profiled segment is derived using Euler theory. The local bulging behavior of the outer steel tube is analyzed with an equivalent beam model. The design recommendations for LPBRB are presented finally.

• Earthquakes and Structures
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• v.23 no.5
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• pp.473-491
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• 2022

The research investigates experimentally the effect of confinement on structural behavior at the ends of beam-column in reinforced concrete (RC) frames. In the experimental study, five specimens consisting of 1/3-scaled RC frames having single-bay, representing the traditional deficiencies of existing buildings constructed without receiving proper engineering service is investigated. The RC frame specimens were produced to represent most of the existing buildings in Turkey that have damage potential. To decrease the probable damage to the existing buildings exposed to earthquakes, the carbon Textile Reinforced Mortar (TRM) strengthening technique (fully wrapping) was used on the ends of the RC frame elements to increase the energy dissipation and deformation capacity. The specimens were tested under reversed cyclic lateral loading with constant axial loads. They were constructed satisfying the weak column-strong beam condition and consisting of low-strength concrete, such as compressive strength of 15 MPa. The test results were compared and evaluated considering stiffness, strength, energy dissipation capacity, structural damping, ductility, and damage propagation in detail. Comprehensive investigations of these experimental results reveal that the strengthening of a brittle frame with fully-TRM wrapping with non-anchored was effective in increasing the stiffness, ductility, and energy dissipation capacities of RC bare frames. It was also observed that the frame-only-retrofitting with an infill wall is not enough to increase the ductility capacity. In this case, both the frame and infill wall must be retrofitted with TRM composite to increase the stiffness, lateral load carrying, ductility and energy dissipation capacities of RC frames. The presented strengthening method can be an alternative strengthening technique to enhance the seismic performance of existing or moderately damaged RC buildings.

• Advances in Computational Design
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• v.8 no.1
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• pp.13-36
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• 2023

The Puebla-Morelos Earthquake (Mw 7.1) occurred in Mexico in 2017 causing 44 buildings to collapse in Mexico City. This work evaluates the non-linear response of a 6-story reinforced concrete (RC) frame prototype model with masonry infill walls on upper floors. The prototype model was designed using provisions prescribed before 1985 and was subjected to seismic excitations recorded during the earthquakes of 1985 and 2017 in different places in Mexico City. The building response was assessed through a damage index (DI) that considers low-cycle fatigue of the steel reinforcement in columns of the first floor, where the steel was modeled including buckling as was observed in cases after the 2017 earthquake. Isocurves were generated with 72 seismic records in Mexico City representing the level of iso-demand on the structure. These isocurves were compared with the location of 16 collapsed (first-floor column failure) building cases consistent with the prototype model. The isocurves for a value greater than 1 demarcate the location where fatigue failure was expected, which is consistent with the location of 2 of the 16 cases studied. However, a slight increase in axial load (5%) or decrease in column cross-section (5%) had a significant detrimental effect on the cumulated damage, increasing the intensity of the isocurves and achieving congruence with 9 of the 16 cases, and having the other 7 cases less than 2 km away. Including column special detailing (tight stirrup spacing and confined concrete) was the variable with the greatest impact to control the cumulated damage, which was consistent with the absence of severe damage in buildings built in the 70s and 80s.

• Steel and Composite Structures
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• v.45 no.3
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• pp.437-454
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• 2022

Elliptic-braced simple resisting frame as a new lateral bracing system installed in the middle bay of frame in building facades has been recently introduced. This system not only creates a problem for opening space from the architectural viewpoint but also improves the structural behavior. Despite the researches on the seismic performance of lateral bracing systems, there are few studies performed on the effect of the stiffness parameters on the elastic story drift and calculation of period in simple braced steel frames. To overcome this shortcoming, in this paper, for the first time, an analytical solution is presented for calculating elastic lateral stiffness in a simple steel frame equipped with elliptic brace subjected to lateral load. In addition, for the first time, in this study, a precise formulation has been developed to evaluate the elastic stiffness variation in a steel frame equipped with a two-dimensional single-story single-span elliptic brace using strain energy and Castigliano's theorem. Thus, all the effective factors, including axial and shear loads as well as bending moments of elliptic brace could be considered. At the end of the analysis, the lateral stiffness can be calculated by an improved and innovative relation through the energy method based on the geometrical properties of the employed sections and specification of the used material. Also, an equivalent element of an elliptic brace was presented for the ease of modeling and use in linear designs. Application of the proposed relation have been verified through a variety of examples in OpenSees software. Based on the results, the error percentage between the elastic stiffness derived from the developed equations and the numerical analyses of finite element models was very low and negligible.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6D
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• pp.895-904
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• 2008

CWR (Continuous Welded Rail) may be broken when a temperature drop below the neutral temperature changes in axial force, causing tensile fracture and rail gap, in winter. Rail-breaks may lead to the damage of the rail and wheel by dynamic load, and the reduction of running safety if not detected before the passage of a train. In this study, the track and train coupled model with open gap for dynamic interaction analysis, is proposed. Linear track and train systems is coupled by the nonlinear Herzian contact spring and the complete system matrices of total track-train system is constructed. And the interaction phenomenon considering open gap, was defined by assigning the irregularity functions between the two sides of a gap. Time history analysis, which have an iteration scheme such as $Newmark-{\beta}$ method based on Modified Newton-Raphson methods, was performed to solve the nonlinear equation. Finally, numerical studies are performed to assess the effect of various parameters of system, apply to various speeds, open gap size and the support stiffness of rail.

• The Journal of Engineering Geology
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• v.3 no.1
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• pp.21-37
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• 1993

In order to investigate the correlation of sedimentary rock properties. specific gravity, porosity, water content, sonic wave velodty, and point4oad strength index of core samples of limestones, sandstones and shales were measured. The relationships between density and velocity show $V_p=16300d-38719.3,{\;}V_s1896.4d-29225.1$ of regression equation for sandstones and $Vp=4085d-10264.8,{\;}V_s=3519d-7841.3$ for shales and <$Vp=4085d^2-20747d+303,{\;}V_s=3899d^2-21442d+318$ for limestones. Seismic wave velocity of shales which have high density is lower than that of sandstones, and this seems to be an effect of bedding in shale. P-wave velocity and S-wave velocity of limestones, sandstones and shales show the linear relationships as a whole. The regression equations are respectively calculated V_s=0.26V_p+1041.6m/sec,{\;}V_s=0.43V_p+424.2m/sec,{\;}and{\;}Vs=0.51V_p+261.9m/sec$ and the correlation coefficients of the velocity show r= 0.86 in sandstones, r= 0.75 in limestones and r=0.86 in shales. According to the point4oad strength test for limestones, point4ord strength anisotropy was not so dear even though the specimens show generally the banded structure. Variations of dip angle of bedding whihin the range $30^{\circ}-60^{\circ}$ does not have much influence upon the diametral strength index and axial strength index. From the result of point load test, P-wave velocity increases with point4ord strength index but the regression equations are $V_p=98.5lI{s_d}+4082.1m/sec,{\;}V_p=106.41{s_a}+3954m/sec$ and their correlation coefficient is low.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1329-1335
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• 2011

On the basis of detailed 3D finite-element (FE) limit analyses, the plastic limit load solutions for pipes with slanted circumferential through-wall cracks (TWCs) subjected to axial tension, global bending, and internal pressure are reported. The FE model and analysis procedure employed in the present numerical study were validated by comparing the present FE results with existing solutions for plastic limit loads of pipes with idealized TWCs. For the quantification of the effect of slanted crack on plastic limit load, slant correction factors for calculating the plastic limit loads of pipes with slanted TWCs from pipes with idealized TWCs are newly proposed from extensive 3D FE calculations. These slant-correction factors are presented in tabulated form for practical ranges of geometry and for each set of loading conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.267-275
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• 2009

The steel pipe of steel-concrete composite piles increases the pile strength and induces the ductile failure by constraining the deformation of the inner concrete. In this research, the load-movement relations and the reinforcement effect by the outer steel pipe in the steel-concrete composite pile were analyzed by performing three-dimensional numerical analyses, which can simulate the yielding behavior of the pile material and the elasto-plastic behavior of soils. The parameters analyzed in the study include three pile materials of steel, concrete and composite, pile diameter and loading direction. As the results, the axial capacity of the composite pile was 1.9 times larger than that of the steel pipe pile and similar with that of the concrete pile. At the allowable movement criteria, the horizontal capacity of the composite pile was 1.46 times larger than that of the steel pile and 1.25 times larger than that of the concrete pile. In addition, the horizontal movement at the pile head of the composite pile was about 78% of that of the steel pile and about 53% of that of the concrete pile, which showed that the movement reduction effect of the composite pile was significant and enables the economical design of drilled shafts.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.213-220
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• 2015

CFT column has a lot of structural advantages due to the composite behavior between in-filled concrete and steel tube. This paper deals with the development of an effective numerical model which can consider the bond-slip behavior between both components of concrete matrix and steel tube without taking double nodes. Since the applied axial load to in-filled concrete matrix is delivered to steel tube by the confinement effect and the friction, the governing equation related to the slip behavior can be constructed on the basis of the force equilibrium and the compatability conditions. In advance, the force and displacement relations between adjacent two nodes make it possible to express the slip behavior with the concrete nodes only. This model results in significant savings in the numerical modeling of CFT columns to take into account the effect of bond-slip. Finally, correlation studies between numerical results and experimental data are conducted to verifying the efficiency of the introduced numerical model.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.796-803
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• 2002

T-shaped walls have different strength, stiffness and ductility in the two opposite directions parallel to the web when subjected to horizontal in-plane loads. When the flange is in tension, the extent that the flange reinforcement contributes to the flexural strength will be subjected to shear-lag effect. Because of this shear-lag effect, the flange may not participate fully in the action with the web, and the effective flange width is needed for predicting the actual strength and stiffness of structures. The objective of this paper is to evaluate the effective flange width and actual strength of the T-shaped wall with Korean code specified detailing of the wall web. Three specimens were tested with cyclic lateral loading applied at top of the wall. A constant axial load of approximately 0.1f$\_$ck/$.$A$\_$g/ is maintained during the testing. Test results show that the effective flange width increases with increasing drift level, such that the entire overhanging flange of h/3 is effective at the maximum strength level. Therefore, the use of PCI or KBC(Korean Building Code) value of h/10 is unconservative with respect to detailing at the wall web boundary.