第三十八卷第二期 (期別148) (112年)
| Title | Effects of chamber geometry on electro-slagwelding failure |
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| Author | Chun-Yao Yang, Keh-Chyuan Tsai |
| Keywords | steel box column, welded moment connection, electro-slag welding,SM570M-CHW steel, flared chamber, finite element model analysis, steel fracture prediction model. |
| Abstract | “In order to transfer the steel beam moment, diaphragm plates are welded inside the box column at the beam flange elevations. Electro-slag welding (ESW) is commonly used to attach the diaphragms to the column. Due to the fabrication imperfection or the frame beam depth difference, eccentricity between beam flange and diaphragm elevations may exist. This situation could lead to brittle fracture initiated at the tip of initial slit near heat affected zone (HAZ). By changing the ESW chamber from a rectangular to a flared cross section, the fusion zone can be increased, but with a price of increasing the thermal input. Considering its advantage of high heat tolerance, SM570M-CHW high strength steel column is considered. This study firstly applied the MM-CVGM fracture prediction model to the tests of two ESW component specimens and seven full-scaled steel beam-to-box column (BC) subassembly specimens conducted in previous studies. Analytical results indicate that the difference between MM-CVGM prediction and test results is no more than one loading cycle, which is more accurate and conservative than the previous model. Additionally, four full-scale BC specimens were fabricated and tested to investigate the effects of chamber geometry and column flange thickness on ESW performance. Results show that the joint with a rectangular ESW failed at the 1.5% inter-story drift ratio (IDR) cycle, while the fractures were delayed until the 4% IDR when the ESW sections were changed to a large or small flared shape. The fracture criterion of the MM-CVGM model was modified in this study. The overall failure initiation is determined by the difference of the first crack initiation between the element and the group. Applying this conditional fracture criterion to the test results, the difference between the prediction and test results is no more than one loading cycle. Circumferential-notched tensile coupon tests were conducted to investigate the ductility difference between the base and weld metals. This study utilized representative volume element models in finite element model analyses. Results show that even the steels are from different sources, very similar failure response can be observed for the same grade of steel with a difference less than 10%. Analytical results indicate that the slope of damage evolution curve of HAZ in the SM570M-CHW base metal is 114% of ESW zone and 88% of CJP zone. Three regions have the same critical damage threshold and the difference is within 5%. When the base metal is changed to SN490C, the critical damage threshold of HAZ is reduced to 29%. Based on the research results, it is recommended that the ESW chamber be considered with a flared section when grade SM570M-CHW or SN490C steel is selected for the column in order to effectively delay the ESW crack initiation.” |
| Title | Experimental Study on the Effect of Crosstie Configuration on the Seismic Performance of Reinforced Concrete Beams |
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| Author | Tai-Kuang Lee, Cheng-Cheng Chen |
| Keywords | reinforced concrete beams, crossties, seismic performance |
| Abstract | “The current Building Code Requirements for Structural Concrete stipulates that in the plastic hinge zone of reinforced concrete beams, the longitudinal reinforcement at each corner and every other longitudinal reinforcement must be enclosed by the corner of the closed hoop or the hooks of crossties used as lateral support. However, in Taiwan reinforced concrete construction practice, the longitudinal reinforcement of RC beams is densely arranged, making construction difficult. In this study, four large-scale reinforced concrete beam specimens were planned and fabricated to conduct experiments to verify the effect of crosstie configuration on the seismic performance of reinforced concrete beams. The transverse reinforcement spacing of S6D and S4D specimens is 6 and 4 times the minimum beam longitudinal reinforcement diameter (D25) respectively, and the longitudinal reinforcements in the middle of the beam are not enclosed with crossties. The transverse reinforcement spacing of S6D-SHB S6D-SHT specimens is 6 times the minimum beam longitudinal reinforcement diameter (D25), the longitudinal reinforcement in the middle is enclosed with crossties, and the seismic hook engages the longitudinal reinforcement at the bottom and the top of the beam, respectively. The total confining force of the transverse reinforcement of S6D-SHB and S6D-SHT specimens (3-D10 reinforcements of SD 280W) is the same as that of S6D specimen (2-D10 reinforcements of SD 420W). It is found that: (1) With respect to the seismic performance in the negative direction (the longitudinal reinforcement at the top of the beam is under tension and the longitudinal reinforcement at the bottom is under compression), the S6D-SHB specimen is the best, the S6D-SHT specimen is second, and the S4D specimen is the third. S6D specimen is the worst. It is because that the middle vertical crosstie is configured in the S6D-SHB specimen and its seismic hook engages the longitudinal reinforcement at the bottom of the beam, delaying the effect of buckling of the longitudinal reinforcement at the bottom. (2) In the same transverse reinforcement total confining force, the ultimate drift angle and plastic rotation angle of the specimen with outer closed hoop and middle vertical crosstie and its seismic hook engaging the longitudinal reinforcement at the bottom of the beam are 5% and 12% higher than those of the specimen with outer closed hoop. It is recommended that during construction, within a range close to 2 times the depth of the beam at the RC beam-column connection, the bottom and side forms are not assembled in advance, and then after the crossties are assembled, the bottom and side forms are installed to solve the construction difficulties. (3) The ultimate drift angle and plastic rotation angle of the specimen with the transverse reinforcement spacing of 4 times the minimum beam longitudinal reinforcement diameter are equal to and 8% higher than those of the transverse reinforcement spacing of 6 times the minimum beam longitudinal reinforcement diameter. The transverse reinforcement spacing of RC beams has no significant effect on the seismic performance of RC beams. (4) Under the same total confining force of transverse reinforcements, when the outer closed hoops and the middle vertical crossties are configured and the seismic hooks engage the longitudinal reinforcement at the bottom of the beam, the ultimate drift angle and plastic rotation angle of the specimen are 5% and 12% higher than those of the specimen with outer closed hoop. When the outer closed hoops and middle vertical crossties are configured and the seismic hooks engage the longitudinal reinforcements at the top of the beam, the ultimate drift angle and plastic rotation angle of the specimen are 2% and 4% higher than those of the specimen with outer closed hoops. This study found that in Section 15.4.3.3 of Building Code Requirements for Structural Concrete, for the plastic hinge zone of RC beams, the rule that the longitudinal reinforcement at each corner and every other longitudinal reinforcement must be enclosed by the corner of the closed hoop or the hooks of crossties used has no significant effect on the seismic performance of RC beams. (5) All four specimens have no significant attenuation in the positive lateral strength, and the negative lateral strength has significant attenuation. In addition, the pinching effect is obvious, and the ultimate drift angle can reach more than 4.0% rad. The required plastic rotation angle is 0.03 rad, so the seismic performance (plastic rotation angle) of all specimens basically does not meet the requirement of 3.0% rad for earthquake-resistant structures. It is speculated that the reason should be caused by flexural-shear failure. (6) For RC beam-column connections, the amount of longitudinal reinforcement at the top is generally slightly greater than the amount of longitudinal reinforcement at the bottom. Therefore, the main failure mode of the T-shaped beam should be the compression failure of the longitudinal reinforcement at the bottom, and the expansion of the closed hoops and crossties. The seismic hook of vertical crosstie engaging the longitudinal reinforcement at the bottom of the beam should also have the effect of delaying the compression and buckling of the longitudinal reinforcement at the bottom.” |
| Title | The Shear Strength of Brick Wall of Window Spandrel |
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| Author | Shuenn-Yih Chang , Hao-En Hung |
| Keywords | Reinforced concrete frame, window spandrel, pushover analysis, failure theory of brick wall, shear strength of brick wall of window spandrel |
| Abstract | The previous experimental study of reinforced concrete frames infilled with brick wall of window spandrel revealed that the shear strength of the brick wall cannot be reliably predicted by the current computing formula. This might result in an unreliable result that is obtained from a pushover analysis. To overcome this difficulty, a series of cyclically loading tests of the eight reinforced concrete frames infilled with this type of brick walls were conducted and thus a new computing formula can be proposed for reliably predicting the shear strength of the brick wall of window spandrel. There are two drawbacks of the current computing formula for predicting the shear strength of brick wall of window spandrel: (1) the height of the infilled brick wall of window spandrel is not considered; and (2) the strength for the rupture of brick is not accounted by the current computing formula for high brick walls of window spandrel. Based on the failure modes of brick walls, the main contributions to shear strength include the horizontal friction force between the mortar and brick, the rupture of motor in vertical direction and the rupture of brick. These two drawbacks will disappear after considering the effect of the ratio of the height over width of brick walls and the rupture of brick for the high brick walls of window spandrel. After modelling the computing formula for predicting the shear strength, a regression analysis is conducted to determine the coefficients of the computing formula based on the test results of eight specimens. To affirm the feasibility of this formula, two test results that were reported in the literature are also compared. Although they adopt the Flemish bond for bricklaying and is different from the use of the English cross bond for the eight specimens for developing the new computing formula, the calculated results are still in good agreement with the test results. |
| Title | Seismic Testing and Design of Steel Panel Dampers |
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| Author | Jin-Ting Lai, An-Chien Wu, Wei-Yang Li, Keh-Chyuan Tsai |
| Keywords | seismic stud column, steel panel damper, shear yielding, web stiffener, seismic design, cyclic loading test |
| Abstract | The 3-segment steel (shear) panel damper (SPD) can be viewed as a type of seismic stud column capable of dissipating energy through inelastic core (IC) shear deformations. In this study, the concept of capacity design is adopted to design a novel SPD with a continuous web plate and doubler plates in the elastic joint (EJ) segments. Considering the IC web buckling resisting stiffeners design guides for SPDs from Japan, and for shear links from the US, this research proposed a simplified design procedure for the IC stiffeners. Cyclic loading tests were conducted on two full-scale 3-segment SPDs with the same EJ doubler plates but different IC web stiffeners. Specimens are 2.6m high and 1.0m deep with a nominal shear strength of 1128kN. Test results show that both specimens had remarkably similar strength and hysteresis response until the 4% inter-story drift ratio was reached. The cumulative plastic deformation index was more than 400. After calibrating the finite element material model, parametric analysis results confirm that the properly deigned plug welds are required for the doubler plates in the EJs thereby delaying shear buckling. Using six additional analysis models for three different target shear deformations of 2%, 4% and 6% radians in the IC segments, it is demonstrated that AISC design specifications on shear link web stiffeners are more conservative and costly. Seismic design recommendations for the IC web stiffeners are concluded. |
| Title | Seismic performance and design of high-rise building incorporating buckling-restrained brace outrigger system |
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| Author | Shou-June Tsai, Pao-Chun Lin |
| Keywords | High-rise structures, outrigger truss systems, buckling beam bracing, nonlinear response spectrum analysis, Nonlinear response yime history analysis |
| Abstract | The keen purpose of this study is to investigate the seismic performance of buildings equipped with damped-outrigger system using the buckling-restrained brace (BRB) system (BRB-outrigger) and to propose the optimal design recommendation for buildings with a different height. The numerical models with building heights of 72, 144, 216 and 288m, each contains two layers of BRB-outrigger and a 40m by 40m structural plan are analyzed using response spectral analysis (RSA) and nonlinear response history analysis (NLRHA) procedures. To get more closer to the actual reality, the member-by-member benchmark models are designed based on the seismic code requirement. In the response spectral analysis procedure, the equivalent damping ratio is computed in order to include the BRB’s inelastic response. For the main purpose of parametric study, a simplified model which will be using a Timoshenko beamcolumn element in order to capture shear-type to flexural-type lateral deformation for a lower to higher raising buildings are proposed. The dimensionless parameters that actually describe the relationships between the core structure stiffness, outrigger flexural stiffness, the axial stiffness of BRB and perimeter column in the parameter study are considered based on practical design and allowable structural sections. The optimization targets include the maximum roof drift, inter-story drift ratio, core structure base shear, core structure overturning moment and the BRB energy dissipation performance. Based on the analyzed result, the ranges of optimal design parameters vary in the different optimization targets and building heights. This study concludes with a design recommendation for building equipped with BRB-outrigger system with different building heights. |