• Title/Summary/Keyword: strength ratios

Search Result 1,624, Processing Time 0.03 seconds

A comparison of three performance-based seismic design methods for plane steel braced frames

  • Kalapodis, Nicos A.;Papagiannopoulos, George A.;Beskos, Dimitri E.
    • Earthquakes and Structures
    • /
    • v.18 no.1
    • /
    • pp.27-44
    • /
    • 2020
  • This work presents a comparison of three performance-based seismic design methods (PBSD) as applied to plane steel frames having eccentric braces (EBFs) and buckling restrained braces (BRBFs). The first method uses equivalent modal damping ratios (ξk), referring to an equivalent multi-degree-of-freedom (MDOF) linear system, which retains the mass, the elastic stiffness and responds in the same way as the original non-linear MDOF system. The second method employs modal strength reduction factors (${\bar{q}}_k$) resulting from the corresponding modal damping ratios. Contrary to the behavior factors of code based design methods, both ξk and ${\bar{q}}_k$ account for the first few modes of significance and incorporate target deformation metrics like inter-storey drift ratio (IDR) and local ductility as well as structural characteristics like structural natural period, and soil types. Explicit empirical expressions of ξk and ${\bar{q}}_k$, recently presented by the present authors elsewhere, are also provided here for reasons of completeness and easy reference. The third method, developed here by the authors, is based on a hybrid force/displacement (HFD) seismic design scheme, since it combines the force-base design (FBD) method with the displacement-based design (DBD) method. According to this method, seismic design is accomplished by using a behavior factor (qh), empirically expressed in terms of the global ductility of the frame, which takes into account both non-structural and structural deformation metrics. These expressions for qh are obtained through extensive parametric studies involving non-linear dynamic analysis (NLDA) of 98 frames, subjected to 100 far-fault ground motions that correspond to four soil types of Eurocode 8. Furthermore, these factors can be used in conjunction with an elastic acceleration design spectrum for seismic design purposes. Finally, a comparison among the above three seismic design methods and the Eurocode 8 method is conducted with the aid of non-linear dynamic analyses via representative numerical examples, involving plane steel EBFs and BRBFs.

Drying Shrinkage Evaluation of Concretes with Various Volume-Surface Ratios, Aggregate Types and Concrete Pavement Mixes (시험체 형상비와 골재종류 및 배합특성에 따른 건조수축 특성평가)

  • Yang, Sung-Chul
    • International Journal of Highway Engineering
    • /
    • v.14 no.1
    • /
    • pp.45-53
    • /
    • 2012
  • This study was performed to analyze test results on drying shrinkage for concrete specimens mixed with various constituents in concrete mixes. Test variables are coarse aggregate types(Limestone, Sandstone, Granite, Andesite, Gneiss), fine aggregate types(natural sand, crushed sand) and cement amounts(normal strength, high strength). Epoxy coating of(U&V-H(A,B)) was applied onto the specimen surface to simulate diverse volume surface ratios(22.2, 40, 85.7, 150, 200, 300) with different specimen sizes. The experiments had been executed during 1,014 days at a condition of $20^{\circ}C$ and relative humidity of 60% in environmental chambers. Test results showed that shrinkage strain from the specimen equivalent to real pavement decreased to 39% compared to the standard specimen recommended by KS. Test results also showed that shrinkage strain of the specimen mixed with Limestone was 56~76% of that with Sandstone, thus Limestone mix seems to be suitable to the concrete pavement.

On the influence of strong-ground motion duration on residual displacement demands

  • Ruiz-Garcia, Jorge
    • Earthquakes and Structures
    • /
    • v.1 no.4
    • /
    • pp.327-344
    • /
    • 2010
  • This paper summarizes results of a comprehensive analytical study aimed at evaluating the influence of strong ground motion duration on residual displacement demands of single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) systems. For that purpose, two sets of 20 earthquake ground motions representative of short-duration and long-duration records were considered in this investigation. While the influence of strong ground motion duration was evaluated through constant-strength residual displacement ratios, $C_r$, computed from the nonlinear response of elastoplastic SDOF systems, its effect on the amplitude and height-wise distribution of residual drift demands in MDOF systems was studied from the response of three one-bay two-dimensional generic frame models. In this investigation, an inelastic ground motion intensity measure was employed to scale each record, which allowed reducing the record-to-record variability in the estimation of residual drift demands. From the results obtained in this study, it was found that long strong-motion duration records might trigger larger median $C_r$ ratios for SDOF systems having short-to-medium period of vibration than short strong-motion duration records. However, taking into account the large record-to-record variability of $C_r$, it was found that strong motion duration might not be statistically significant for most of the combinations of period of vibration and levels of lateral strength considered in this study. In addition, strong motion duration does not have a significant influence on the amplitude of peak residual drift demands in MDOF systems, but records having long strong-motion duration tend to increase residual drift demands in the upper stories of long-period generic frames.

Aspects of size effect on discrete element modeling of normal strength concrete

  • Gyurko, Zoltan;Nemes, Rita
    • Computers and Concrete
    • /
    • v.28 no.5
    • /
    • pp.521-532
    • /
    • 2021
  • Present paper focuses on the modeling of size effect on the compressive strength of normal concrete with the application of Discrete Element Method (DEM). Test specimens with different size and shape were cast and uniaxial compressive strength test was performed on each sample. Five different concrete mixes were used, all belonging to a different normal strength concrete class (C20/25, C30/37, C35/45, C45/55, and C50/60). The numerical simulations were carried out by using the PFC 5 software, which applies rigid spheres and contacts between them to model the material. DEM modeling of size effect could be advantageous because the development of micro-cracks in the material can be observed and the failure mode can be visualized. The series of experiments were repeated with the model after calibration. The relationship of the parallel bond strength of the contacts and the laboratory compressive strength test was analyzed by aiming to determine a relation between the compressive strength and the bond strength of different sized models. An equation was derived based on Bazant's size effect law to estimate the parallel bond strength of differently sized specimens. The parameters of the equation were optimized based on measurement data using nonlinear least-squares method with SSE (sum of squared errors) objective function. The laboratory test results showed a good agreement with the literature data (compressive strength is decreasing with the increase of the size of the specimen regardless of the shape). The derived estimation models showed strong correlation with the measurement data. The results indicated that the size effect is stronger on concretes with lower strength class due to the higher level of inhomogeneity of the material. It was observed that size effect is more significant on cube specimens than on cylinder samples, which can be caused by the side ratios of the specimens and the size of the purely compressed zone. A limit value for the minimum size of DE model for cubes and cylinder was determined, above which the size effect on compressive strength can be neglected within the investigated size range. The relationship of model size (particle number) and computational time was analyzed and a method to decrease the computational time (number of iterations) of material genesis is proposed.

A Study on the Shear Behavior of Recycled Aggregate Reinforced Concrete Beams without Stirrups (전단보강이 없는 순환골재 철근콘크리트 보의 전단거동에 관한 연구)

  • Lee, Jung-Hoon;Kim, Woo-Suk;Baek, Seung-Min;Kang, Thomas H.K.;Kwak, Yoon-Keun
    • Journal of the Korea Concrete Institute
    • /
    • v.25 no.4
    • /
    • pp.389-400
    • /
    • 2013
  • Little investigations have been carried out to study the shear behaviors of RC beams with recycled aggregates. So, this experiment investigates the shear performance and suggests the possible application of Recycled Concrete Aggregate (RCA) for building structures. In general, shear strength of reinforced concrete beam without stirrups is dependent on the compressive strength of concrete, the longitudinal steel ratio, and the shear span-to-depth ratio. In this study, total 28 recycled aggregate concrete beams without shear reinforcement were tested by two-point load and all beams were singly reinforced. The variables studied in this investigation are shear span-to-depth ratios (a/d=2, 3 and 4), RCA replacement ratios (0, 15, 30 and 50%) and longitudinal steel ratios (0.80, 1.27 and 1.84%). The designed concrete compressive strength with a 30 MPa is used. This research will play an important role toward the establishment of the structural design standard for RCA concrete.

Evaluation of Characteristics of Shear Strength and Poisso's Ratio through Triaxial and Bender Element Tests (벤더엘리먼트와 삼축시험을 통한 모래의 전단강도 및 포아송비 특성 규명)

  • Yoo, Jin-Kwon;Park, Du-Hee
    • Journal of the Korean Geotechnical Society
    • /
    • v.30 no.5
    • /
    • pp.67-75
    • /
    • 2014
  • In this paper, isotropically consolidated drained triaxial compression test device installed with bender elements is used to measure stress, stain, and shear wave velocity, from which the characteristics of shear strength and Poisson'ratio are investigated. The results show that there is a unique relationship between maximum shear modulus determined from shear wave velocity and effective vertical stress at failure, which is defined as the sum of vertical and radial stresses at failure. The correlation is very useful since it is possible to predict the shear strength and internal friction angle from shear wave velocity. In addition, Poisson's ratio is determined from measured axial and volumetric strains. It is demonstrated that the range of measured Poisson's ratio is between 0.15 and 0.6, and increases with the axial strain. The ratios at axial strains smaller than 0.2% corresponds to the range recommended in design codes, which are approximately from 0.3~0.35. However, at axial strains exceeding 1%, the measured ratios are between 0.5 and 0.6. It is therefore shown that use of ratios commonly used in practice will result in pronounced underestimation at large strains.

The Inhibition Effect of Alkali-Silica Reaction in Concrete by Pozzolanic Effect of Metakaolin (메타카오린의 포조란 효과에 의한 콘크리트 내 알칼리-실리카 반응 억제 효과)

  • Lee Hyomin;Jun Ssang-Sun;Hwang Jin-Yeon;Jin Chi-Sub;Yoon Jihae;Ok Soo Seok
    • Journal of the Mineralogical Society of Korea
    • /
    • v.17 no.3
    • /
    • pp.277-288
    • /
    • 2004
  • Alkali-silica reaction (ASR) is a chemical reaction between alkalies in cement and chemically unstable aggregates and causes expansion and cracking of concrete. In the Present study, we studied the effects of metakaolin, which is a newly introduced mineral admixture showing excellent pozzolainc reaction property, on the inhibition of ASR. We prepared mortar-bars of various replacement ratios of metakaolin and conducted alkali-silica reactivity test (ASTM C 1260), compressive strength test and flow test. We also carefully analyzed the mineralogical changes in hydrate cement paste by XRD qualitative analysis. The admixing of metakaolin caused quick pozzolanic reaction and hydration reaction that resulted in a rapid decrease in portlandite content of hydrated cement paste. The expansion by ASR was reduced effectively as metakaolin replaced cement greater than 15%. This resulted in that the amounts of available portlandite decreased to less than 10% in cement paste. It is considered that the inhibition of ASR expansion by admixing of metakaolin was resulted by the combined processes that the formation of deleterious alkali-calcium-silicate gel was inhibited and the penetration of alkali solution into concrete was retarded due to the formation of denser, more homogeneous cement paste caused by pozzolanic effect. Higher early strength (7 days) than normal concrete was developed when the replacement ratios of metakaolin were greater than 15%. And also, late strength (28 days) was far higher than normal concrete for the all the replacement ratios of metakaolin. The development patterns of mechanical strength for metakaolin admixed concretes reflect the rapid pozzolanic reaction and hydration properties of metakaolin.

Interaction of internal forces of interior beam-column joints of reinforced concrete frames under seismic action

  • Zhou, Hua;Zhang, Jiangli
    • Structural Engineering and Mechanics
    • /
    • v.52 no.2
    • /
    • pp.427-443
    • /
    • 2014
  • This paper presents detailed analysis of the internal forces of interior beam-column joints of reinforced concrete (RC) frames under seismic action, identifies critical joint sections, proposes consistent definitions of average joint shear stress and average joint shear strain, derives formulas for calculating average joint shear and joint torque, and reports simplified analysis of the effects of joint shear and torque on the flexural strengths of critical joint sections. Numerical results of internal joint forces and flexural strengths of critical joint sections are presented for a pair of concentric and eccentric interior connections extracted from a seismically designed RC frame. The results indicate that effects of joint shear and torque may reduce the column-to-beam flexural strength ratios to below unity and lead to "joint-yielding mechanism" for seismically designed interior connections. The information presented in this paper aims to provide some new insight into the seismic behavior of interior beam-column joints and form a preliminary basis for analyzing the complicated interaction of internal joint forces.

Parametric Study on the Joint Strength of Unidirectional and Fabric Hybrid Laminate (일방향-평직 복합재 혼합 적층판의 기계적 체결부 강도에 관한 인자연구)

  • 안현수;신소영;권진회;최진호;이상관;양승운
    • Proceedings of the Korean Society For Composite Materials Conference
    • /
    • 2002.05a
    • /
    • pp.9-12
    • /
    • 2002
  • A parametric study has been conducted to investigate the effect of the geometry on the strength of an unidirectional and fabric hybrid laminated composite joint. Tests are conducted for the specimens with nine different edge-to-hole diameter or width-to-hole diameter ratios. For the finite element analysis, the characteristic length method is used, and the tests for determining the characteristic length are performed additionally. Nonlinear contact problem between the pin and laminate is modeled by the gap element in MSC/NASTRAN. Tsai-Wu failure criteria is applied to the stress on the characteristic curve. The finite element and experimental results shows good agreement in strength of composite joint. Results of the parametric study shows the effect of the geometry is remarkable in the specimens with width-to-hole diameter ratio less than 2.8 and edge-to-hole diameter ratio less than 1.4.

  • PDF

A Study on the Waterproof Properties of Cement Mortar with the Addition Rate of the Inorganic Admixture and Zinc Stearate (무기질 혼화재 및 금속비누의 혼입률 변화에 따른 시멘트 모르터의 방수 특성에 관한 연구)

  • Choi, Hoon;Jiang, Yi-Long;Han, Min-Cheol;Ryu, Hyun-Ki;Han, Cheon-Goo
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • 1998.10c
    • /
    • pp.139-144
    • /
    • 1998
  • This study is intended to devolop the self waterproof agents for high performance concrete by analyzing the properties of fresh and hardened mortar with various addition ratios of the inorganic admixture and zinc stearate. As the results of the test, the flow and air content increase with the addition of expansive additives. When the replacement rate of silica fume increases, the flow decreases for the increased viscidity. And the flow and sir content decrease with the addition of zinc stearate. At hardened state, the compressive strength, tensile strength and flexual strength decrease with the addition of expansive additives and zinc stearate. With the increase of silica fume's replacement, they show a little decrease at early age and then increase gradually. Also, absorption and permeability show a steep decrease when zinc stearate is added, and a slack decrease with the replacement of silica fume.

  • PDF