Allowable Compressive Stress Research Articles

Investigation on allowable compressive stresses in pretensioned concrete members at transfer

Modern structural concrete members have become longer and slender, and the prestressed concrete method is an efficient way for sufficiently satisfying the strength and serviceability requirements of such members. Particularly, pretensioned concrete members are typically produced as a precast system that can reduce the construction time and waste significantly by minimizing on-site work. Thus, the pretensioned precast concrete structure is an effective method that can meet both environmental and economic demands in international society. Productivity of the pretensioned members, however, is significantly influenced by the timing of releasing prestress, because prestressing forces can be transferred when the target compressive strength of early age concrete is attained. Unfortunately, the allowable compressive stress at transfer specified in current design code provisions may not be reliable in some practical situations, and those stress limits were determined by empirical methods without a theoretical basis. To overcome such problems, a reasonable estimation equation for allowable compressive stress at transfer was proposed in this paper using extensive analyses based on the Strength Design Method (SDM), in which the eccentricity ratio of the tendon, the sectional size and shape, the level of prestress, and the self-weight moment were considered. The allowable releasing compressive stresses specified in international design codes and based on the proposed equation were compared to test results collected from literature. These comparisons indicated that the allowable stresses specified in current design codes provided unconservative evaluation results for pretensioned members with low eccentricity ratios and conservative results for those with high eccentricity ratios, while the proposed equation reasonably evaluated the allowable compressive stresses of pretensioned members with rectangular, tee, and inverted tee sections.

Buckling of Cylindrical, Thin Wall, Trailer Truck Tanks and ASME Section XII

New hazmat (hazardous material) and nonhazmat transport tanks will be constructed to the rules of the ASME Code Section XII (ASME Boiler and Pressure Vessel Code, American Society of Mechanical Engineers, 3 Park Avenue, New York, NY 10016-5990). The criteria and basis to design these tanks have been questioned and a full scale buckling test has been performed to evaluate maximum allowable over-the-road loadings and required design details. This paper summarizes the results of this testing and provides comparisons with classical Code buckling criteria, Code Case 2286-2 (ASME Code Case 2286-2, Cases of ASME Boiler and Pressure Vessel Code, Case 2286-2, “Alternative Rules for Determining Allowable Compressive Stresses for Cylinders, Cones, Spheres, and Formed Heads”) and other methods for such evaluations. The objective is to provide the ASME Section XII committee with a basis for establishing buckling design criteria and shell stiffening details for both hazmat and nonhazmat transport tanks.

A study on the ultimate performances of elastomeric bearings in Korea

As part of the efforts to improve the performances and reliability of the elastomeric bearings produced in Korea, this paper evaluates experimentally the validity of the ultimate loads of the design allowable values of KS F 4420 purposed for the design of elastomeric bearings in Korea. To that goal, a series of tests including ultimate compression test, ultimate shear test and shear fatigue test were conducted on elastomeric bearings designed in compliance with KS F 4420. The results showed that failure occurred at loads 16 to 26 times larger than the allowable compressive stress and made it possible to conclude that the so-designed elastomeric bearings secured sufficient reliability regard to the vertical performance. In the case of the shear performance, the elastomeric bearings failed in a load range larger than the allowable design values but the performances were also seen to fluctuate sensitively according to the fabrication conditions of the bearings. Especially, the tests revealed that the shear performance degraded significantly or that early failure occurred when the internal rubber layer of the bearings were not fabricated using a single rubber layer. Since the elastomeric bearing can be used in the seismic design complementarily to seismic devices, even if it is not a seismic isolator, the bearing should secure high shear performance. The routine by which some companies are fabricating the internal rubber layer by stacking several rubber pads to form one layer is not only degrading the performance of the elastomeric bearing but may also provoke unexpected failure. This stresses the need for the establishment of specifications forbidding such customary practice.

G191012 張力場解析と座屈解析によるインフレータブルビームのしわ発生後の応力場の比較([G191]宇宙工学部門,一般セッション)

Geometrically nonlinear finite element analyses of inflated beams are conducted to study the distributions of stress fields after wrinkling with various section parameters.The results show that the minor principal stress fields at the bottom of the beams after wrinkling are almost constant,which gives an allowable constant compressive stress parameter in the modified tension field theory.A parametric study of cross sections of inflated beams is conducted to identify the characteristics of the constant parameter.

프리텐션된 콘크리트 부재의 프리스트레스 도입시 허용압축응력에 관한 실험적 연구

선행연구에서는 강도이론을 바탕으로 영향인자들을 반영한 해석단면에 대해 허용압축응력(<TEX>$Kf_{ci}$</TEX>)을 해석하였고, 해석결과를 바탕으로 허용압축응력산정식을 제안하였다. 이전 연구에 대한 일련의 연구로서, 본 연구에서는 서로 다른 편심비(e/h)를 갖는 프리텐션 보 부재에 대한 프리스트레스 도입 실험을 수행하였다. 실험결과를 토대로 제안식을 검증한 결과 낮은 e/h를 갖는 프리텐션 부재의 경우, ACI318-08 및 EC2-02의 설계기준이 <TEX>$Kf_{ci}$</TEX>를 비안전측으로 결정하고 있음을 확인하였다. 또한 높은 e/h를 갖는 프리텐션 부재의 경우 현행의 설계기준은 <TEX>$Kf_{ci}$</TEX>를 과도하게 안전측으로 제안하고 있다. 이에 비해 제안식은 e/h에 따른 <TEX>$Kf_{ci}$</TEX>를 합리적으로 평가하는 것으로 나타났다. In the previous research, allowable compressive stress was analyzed based on strength theory, in which primary effect factors on the allowable compressive stress, such as eccentricity ratio, section type, section size, prestress and self-weight moment, were considered. As its results, allowable compressive stress equations were proposed. As a series of the previous research, this paper presents an experimental study on the prestress at transfer of pre-tensioned members with different eccentricity ratios. The results shows that ACI318-08 and EC2-02 are unconservative for the members under low eccentricity ratios, and they are conservative for the members under high eccentricity ratios. Compared to the code provisions, the results indicates that the proposed equation reasonably well evaluates the allowable compressive stresses for those with different eccentricity ratios.

T형 및 역T형 단면을 가지는 프리텐션부재의 프리스트레스 도입시 허용 압축응력

이 연구의 선행 연구에서는 강도 이론을 바탕으로 장방형 단면을 갖는 프리텐션 부재의 허용 압축응력 계수 산정식을 제안하였다. 이 연구에서는 프리스트레스 도입시 T형 단면 및 역T형 단면을 갖는 프리텐션 부재의 허용 압축응력 계수를 결정하기 위하여 선행 연구에서 적용한 강도 이론을 바탕으로 단면의 크기, 단면 형상, 긴장재량 및 편심비를 고려한 방대한 해석을 수행하였다. 해석 결과를 바탕으로 허용 압축응력 계수 산정식을 유도하였으며, 제안된 산정식은 프리스트레스 도입시 허용 압축응력을 T형 및 역T형 단면에서 각각 당시 콘크리트 압축강도의 80% 및 70%로 제한하였고 이는 기존의 설계기준들에서 제공하는 값보다 높은 수치였다. 제안식을 검증하기 위하여 기존의 수행된 실험 결과 및 각국의 설계기준과 비교한 결과, 낮은 편심비에서 국내ㆍ외 기준은 비안전측의 결과를, 높은 편심비에서는 오히려 과도하게 안전측의 결과를 제공할 수 있는 것으로 나타났으며, 이에 비해 제안식은 T형 및 역 T형단면을 갖는 프리텐션 부재의 허용 압축응력을 매우 합리적으로 평가하였다.

High-strength self-consolidating concrete girders subjected to elevated compressive fiber stresses, part 2: Structural behavior

The design of prestressed concrete members is restricted by the requirement that the extreme compressive fiber stress at midspan be less than 60% of the concrete compressive strength at release of prestressing. The purported purpose of this limit is to provide serviceability performance, but it places unnecessary limits on the capability of the materials. For this research program, 6 prestressed concrete girders were produced with high-strength, self-consolidating concrete and subjected to elevated compressive fiber stress levels ranging from 65% to 84% of initial concrete compressive strength at release of prestressing. Part 1 of this series analyzed time-dependent prestress losses and camber behavior and compared these values with the results from typical prediction methods. This second part examines the flexural and shear behavior of the same girders. The results of structural testing indicated little reduction in flexural capacity of girders subjected to elevated stress levels, but further testing in shear is needed to reduce the variability in the results. The results reported here suggest that an increase in the allowable compressive stress limit up to at least 70% of the initial concrete compressive strength at release of prestressing at any location is feasible.

High-strength self-consolidating concrete girders subjected to elevated compressive fiber stresses, part 1: Prestress loss and camber behavior

The design of prestressed concrete members is restricted by the requirement that the extreme compressive fiber stress at midspan of simply supported members be less than 60% of the concrete compressive strength at release of prestressing. The purported purpose of this limit is to address serviceability performance, but it places unnecessary limits on the capability of the materials. For this research program, six prestressed concrete girders were produced with high-strength self-consolidating concrete and subjected to compressive fiber stress levels ranging from 65% to 84% of the concrete compressive strength at release of prestressing. Time-dependent concrete surface strains were measured using a mechanical strain gauge, with a focus on measuring drying creep and determining its relationship to prestress losses. This research demonstrates that current American Association of State Highway and Transportation Officials load and resistance factor design prestress-loss prediction methods developed for high-strength concrete overestimate losses by 18%, whereas older methods for prestress losses developed for normal-strength concrete produced more-accurate results. Based on these results and work performed by others, the authors concur with increasing the allowable compressive stress limit at any location to 70% of the concrete compressive strength at release of prestressing.

Multicriteria Capacity Envelopes for Biaxial Bending of Concrete Hydraulic Structures

Envelopes for biaxial bending capacity of reinforced concrete elements are used extensively in design or in structural safety evaluation to verify the adequacy of internal force resultants from series of axial P and bending moments M x and M y loading pairs computed for prescribed load combinations. However, existing methods to construct P-M x -M y (PMM) interaction curves are not appropriate for concrete hydraulic structures because (1) pressurized water could penetrate in cracks leading to a coupled hydromechanical problem and (2) the structural performance is assessed using several criteria related to the allowable cracked area as well as allowable compressive (tensile) stresses for usual, unusual, and extreme load combinations. This paper presents a methodology to construct PMM interaction curves for arbitrary cross sections of hydraulic structures considering multiperformance criteria, water penetration in cracks, as well as the presence of reinforcing steel. The computations are based on a robust and efficient isogonic approach based on strength of materials where the position of the neutral axis is systematically varied over the cross section to find PMM equilibrium solutions. Four application examples of the proposed approach are presented (1) to illustrate its versatility, (2) to validate the results, and (3) to show its convergence properties. In some cases, PMM capacity envelopes are formed by distinct closed surfaces where equilibrium solutions are possible. This type of PMM capacity envelope, which the proposed algorithm is able to construct, is not found for classical reinforced concrete elements.

Effects of Increasing Allowable Compressive Stress at Prestress Transfer

This paper evaluates the benefits and weaknesses of increasing the allowable compressive stress at prestress transfer in prestressed concrete members. A historical background of the allowable release stress in compression is provided. A simple design example is used to quantify potential production and design benefits of increasing the allowable stress and the applicability of these benefits is discussed. Test results of 36 pretensioned beams that were subjected to a range of maximum compressive stresses at release are reported and analyzed. The results suggest that the compressive stress limit at prestress transfer must govern the design of the pretensioned member to achieve significant production or design benefits from increasing the allowable stress, but that production and design benefits cannot be maximized simultaneously. The findings indicate that although increasing the allowable release stress in compression at midspan of a member to 0.65fci' or 0.70fci' is possible, members subjected to midspan release stresses in excess of 0.70fci' displayed premature flexural cracking. Before design codes are changed, however, additional testing on full-scale specimens is recommended.

Design Margin of Allowable Compressive Stresses for Knuckle Plate of Refrigerated Storage Tank

Design Margin of Allowable Compressive Stresses for Knuckle Plate of Refrigerated Storage Tank

157 低温貯蔵タンクナックルプレートの許容圧縮応力

157 低温貯蔵タンクナックルプレートの許容圧縮応力

Structural Design of 80-Story RC High-Rise Building Using 200 Mpa Ultra-High-Strength Concrete

This paper presents the design of an 80-story reinforced concrete (RC) high-rise building using 200 MPa ultra-high-strength concrete. Static nonlinear push over analyses, Level-1 and Level-2 nonlinear earthquake response analyses and nonlinear wind response analyses were carried out. Based on the three-dimensional static nonlinear analyses of the building subjected to design earthquake loading in two principal directions, the obtained maximum axial load ratio for the first story columns of 200 MPa compressive strength concrete were 0.53 and 0.48, respectively, at the ultimate limit state, which meets the design criterion based on the allowable compressive stress of concrete. The maximum story drift angle obtained under the synthetic wave motion at the construction site was smaller than the design limiting value of 1/100. While yield hinges developed only in some of the short beams, no yield hinge in columns was observed. The maximum ductility of 1.28 obtained in the beams is lower than the design limiting value of 4.0. The maximum story shear force for the level-2 wind load was almost half that of the level-2 earthquake load when using the lumped-mass model. The analyses confirmed that the use of 200 MPa concrete enables structural designers to provide the member sections with adequate sizes comparable to that of ordinary high-rise RC buildings. The analytical results showed that the performance of the building satisfies the design criteria for serviceability limits, design limits and ultimate limits.

Michell cantilevers constructed within trapezoidal domains—Part I: geometry of Hencky nets

The present paper is the first part of the four-part work on Michell cantilevers transmitting a given point load to a given segment of a straight-line support, the feasible domain being a part of the half-plane contained between two fixed half-lines. The axial stress σ in the optimal cantilevers is assumed to be bounded by −σ C ≤σ≤σ T , where σ C and σ T represent the allowable compressive and tensile stresses, respectively. The work provides generalization of the results of the article of Lewinski et al. (Int J Mech Sci 36:375–398, 1994a) to the case of σ T ≠σ C . The present, first part of the work concerns the analytical formation of the Hencky nets or the lines of fibres filling up the interior of the optimal cantilevers corresponding to an arbitrary position of the point of application of the given concentrated force.

Effect of Allowable Compressive Stress at Release on Prestress Losses and on the Performance of Precast, Prestressed Concrete Bridge Girders

This paper presents the results of a research program that examined prestress losses in high-performance concrete bridge girders and the effects, if any of compressive stresses at release exceeding the current allowable stress limit of 0.60 f' ci . Four I-shaped girders were cast and tested with compressive release stresses ranging from 0.57 f' ci to 0.82 f' ci . Two of the four girders were made with air-entrained concrete; prestress losses were measured on these as well and compared with losses in girders made with non-air-entrained concrete. The measured prestress losses were then compared with prestress losses estimated using: (1) the 2004 American Association of Highway Transportation Officials load-resistant factor design (AASHTO LRFD) Bridge Design Specifications (refined method), (2) the PCI Design Handbook method described by Zia et al., and (3) the method proposed in the National Cooperative Highway Research Program (NCHRP) Report 496 (detailed method). Of the three methods to estimate losses, the NCHRP Report 496's Detailed Method for Estimating Prestress Losses most accurately predicted the measured losses, followed by the Zia et al. equations, and then the 2004 AASHTO LRFD equations. A second objective of the research was to provide additional data measuring prestress losses for cases where the actual compressive stresses at release exceed the allowable compressive stresses at release. The research results support increasing the allowable compressive stress at release from 0.60 f' ci to 0.70 f' ci .

Effect of support compliance and residual stress on the shape of doubly supported surface-micromachined beams

Doubly supported silicon-micromachined beams are increasingly used to study the mechanical properties of materials. Residual stresses in the beams and support compliance cause significant vertical deflections, which affect the performance of these micromachined devices. We present here both experimental results for doubly supported polysilicon surface-micromachined beams, and an elastic model of the devices that takes into account the compliance of the supports and the geometrical nonlinear dependence of the vertical deflections on the stress in the beam. An elastic one-dimensional model was used for the beams, and the response of the supports to forces and moments was obtained using finite-element method simulations. The model explains a previously observed gradual increase of the maximum vertical deflections of the beams with increasing length at a given constant residual stress and, in agreement with experimental observations, predicts two stable states for compressively stressed beams: one with the beam bent up, the other down. We introduce a critical biaxial residual stress /spl sigma/r/sub c/, above which there are significant deflections of the beams, /spl sigma//sub rc/ can be used in practice to determine the maximum allowable compressive biaxial residual stress as a function of the beam length. The effect of variations of the compliance of the supports is reported.

Axial mechanical properties of epoxy impregnated superconducting solenoids at 4.2 K

The mechanical properties of superconducting solenoids along their longitudinal axes were characterized at 4.2 K through a series of tests on small epoxy impregnated coils. Three coil configurations were manufactured which consisted of two layers of either Nb/sub 3/Sn or NbTi. The Nb/sub 3/Sn conductor was insulated with E-Glass fiber braid insulation and the NbTi conductor was insulated with either polyester braid or Polyvinylformal (FORMVAR). Characteristics including the elastic modulus, allowable compressive stress, cyclic loading behavior, and, of primary interest, ultimate tensile strength were measured. Samples were compressed to 200 MPa and fatigued 100 cycles from -125 MPa to 25 MPa. The tensile strengths are shown to be dependent of the insulation material and range from 51.9 MPa to 62.8 MPa.

Serviceability Design of Prestressed Concrete Bridges

In this paper, serviceability limit states of prestressed concrete bridges are examined. Allowable compressive and tensile stresses in concrete under service loads are first used to determine the upper and lower limits of the longitudinal prestressing force. The same allowable stresses are used to define allowable shear stresses that prevent excessive tensile stresses in the principal tensile stress direction and that prevent excessive compressive stresses in the principal compressive stress direction. In some cases where the shear stresses due to service loads exceed the allowable shear stress, shear cracking may be controlled by transverse prestressing of the webs. Equations are presented to determine the required transverse prestressing force. An example concludes the paper.

許容めり込み応力度に関する検討と提案 : 木材の繊維に直角方向の圧縮に関する研究

In this paper, we carried out loading test and finite element analysis, and studied the behavior of partial compression perpendicular to grain considering the distance from the end of member to the bearing area, the depth of member and the bearing length in order to investigate suitability of the allowable partial compressive stress perpendicular to grain of Japanese standard for member with large cross-sectional area like Heavy Timber. As a result, we clarified that the allowable partial compressive stress perpendicular to grain of Japanese standard wasn't reasonable for the actual behavior of partial compression perpendicular to grain, and suggested new leading method using modulus of apparent elasticity, strain-energy and the ratio between depth of member arid bearing length as the parameter, and the concrete numerical value for the allowable partial compressive stress perpendicular to grain.

Optimal discrete sizing of truss structures subject to buckling constraints

The selective dynamic rounding (SDR) algorithm previously developed by the authors, and based on a dual step rounding approach, is used for the optimal sizing design of truss structures subject to linear buckling constraints. The algorithm begins with a continuous optimum followed by a progressive freezing of individual variables while solving the remaining continuous problems. The allowable member stresses are predicted by the linear regression of the tabular section properties, while the exact allowable compressive stresses are back-substituted for those variables fixed on discrete values in each intermediate mixed-discrete nonlinear problem. It is shown that a continuous design based on the regression analysis of section effectiveness vs. area is effective as a starting point for the dual step discrete optimization phase. A range of examples is used to illustrate that with “conservative” regression, discrete designs can be achieved which are significantly lighter than those in which the variables have been rounded up.