Pretension Load Research Articles

Cable-pulley brace to improve story drift distribution of MRFs with large openings

This study aims to introduce a new bracing system by which even super-wide frames with large openings can be braced. The proposed system, hereafter called Cable-Pulley Brace (CPB), is a tension-only bracing system with a rectilinear configuration. In CPB, a wire rope passes through a rectilinear path around the opening(s) and connects the lower corner of the frame to its opposite upper one. CPB is a secondary load resisting system with a nonlinear-elastic hysteretic behavior due to its initial pre-tension load. As a result, the required energy dissipation would be provided by the MRF itself, and the main intention of using CPB is to contribute to the initial and post-yield stiffness of the whole system. Using a stiffness calibration technique, optimum placement of the CPBs is discussed to yield a uniform displacement demand along the height of the structure. A displacement-based design procedure is proposed by which the MRF with CPB can be designed to achieve a uniform distribution of inter-story drifts with predefined values. Obtained results indicated that CPB leads to significant reductions in maximum and residual deformations of the MRF at the expense of minor increase in the maximum base shear and developed axial force demands in the columns. In the case of a typical 5-story residential building, compared to SMRF system, CPB system reduces maximum amounts of inter-story and residual drifts by 35% and 70%, respectively. Moreover, openings of the frame are not interrupted by the CPB. This is the most appealing feature of the proposed bracing system from architectural point of view.

Nonlinear elasto-plastic analysis of slack and taut cable structures

This paper presents the geometrically nonlinear analysis of the slack and taut cable structures considering the material inelasticity subjected to self-weight, pretension, and external loads. The finite element procedure is briefly summarized using the Lagrangian formulation associated with isoparametric interpolation polynomials and the Newton---Raphson iterative scheme with incremental load. The simple and efficient method to determine the initial equilibrium state of the slack cable systems under self-weight as well as support motions is presented using the penalty method. The numerical algorithm to evaluate the tangent modulus of elasticity of cable is presented based on the iterative scheme. The accuracy and reliability of the present study are verified by comparing the predictions with those generated by well-reported slack and taut cable structure problems. The effect of the yielding of cable segments on displacements and stresses of cable structures is investigated.

Toward buckling free tension-only braces using slack free connections

This study introduces a slack free connection (SFC) by which pinching would be removed from hysteretic behavior of tension-only braces (TOBs). SFC through its mono-directional behavior, eliminates undesirable pinching of the tension-only bracing and changes it to a reliable lateral load resisting system with high energy dissipation capability. A Matlab/Simulink-based model, called Macro-Simulink model, is developed to simulate hysteretic behavior of TOBs with or without SFC. Derived Macro-Simulink model is also able to account for hysteretic behavior of the frame. The frame itself can have either deteriorated or non-deteriorated hysteretic behaviors. The Macro-Simulink model is verified through different techniques including earlier experimental results, explicit finite element modeling, and other pre-verified analytical/numerical tools. It is observed that initial pre-tension load only affects initial stiffness of the TOB and has no contribution on its nonlinear hysteretic behavior. Obtained results of this study indicate that energy dissipation capacity of TOBs with SFC would be improved up to 6 times compared with that of conventional TOBs. Moreover contribution of SFC is more pronounced in the case of frames with highly deteriorated behaviors. As a result TOB with SFC can be considered for retrofit purposes as well.

Comparative Analysis of Three Kinds of Mega Steel Frame System Static Performance

Mega steel structure because of its own advantages is widely used in high-rise buildings, especially in super high-rise buildings. Mega frame structure, mega steel frame-prestressed composite bracing structure and mega steel frame-cable bracing structure were analyzed in this paper. The structure deformation and internal force of beam and column of structures were studied under load combination of Pretension and vertical loads, horizontal wind load. The results show that prestressed cable can improve the system stiffness, make the overall stiffness more uniform and control the deflection of mega beam and axial force of mega column effectively.

Dynamic High-Temperature Tensile Characterization of an Iridium Alloy with Kolsky Tension Bar Techniques

Conventional Kolsky tension bar techniques were modified to characterize an iridium alloy in tension at elevated strain rates and temperatures. The specimen was heated to elevated temperatures with an induction coil heater before dynamic loading; whereas, a cooling system was applied to keep the bars at room temperature during heating. A preload system was developed to generate a small pretension load in the bar system during heating in order to compensate for the effect of thermal expansion generated in the high-temperature tensile specimen. A laser system was applied to directly measure the displacements at both ends of the tensile specimen in order to calculate the strain in the specimen. A pair of high-sensitivity semiconductor strain gages was used to measure the weak transmitted force due to the low flow stress in the thin specimen at elevated temperatures. The dynamic high-temperature tensile stress–strain curves of a DOP-26 iridium alloy were experimentally obtained at two different strain rates (~1000 and 3000 s−1) and temperatures (~750 and 1030 °C). The effects of strain rate and temperature on the tensile stress–strain response of the iridium alloy were determined. The iridium alloy exhibited high ductility in stress–strain response that strongly depended on strain-rate and temperature.

A theoretical and experimental investigation on large amplitude free vibration behavior of a pretensioned beam with clamped–clamped ends using modified homotopy perturbation method

In this study, large amplitude free vibration behavior of a pretensioned Euler–Bernoulli beam is investigated both theoretically and experimentally. The Hamilton's principle is used to derive the beam governing equation of motion. By implementing the Galerkin's method and assuming the clamped–clamped boundary condition, the partial differential equation is converted to an ordinary nonlinear differential equation. Because of the large coefficient of the nonlinear term, the new homotopy perturbation method proposed by He, is modified to solve the governing nonlinear equation. Comparing the first- and the second-order approximate solutions of the modified homotopy perturbation method (MHPM) and those available in the literature demonstrates that the second-order MHPM leads to a more accurate solution which is valid for a wide range of the vibration amplitudes. The results have been validated by the experimental tests and the MHPM method. Also, the results show that an increase in the vibration amplitude and/or the pretension load increases the fundamental resonance frequency ratio. Besides, it would decrease with increasing the beam slenderness ratio.

Dynamic high-temperature Kolsky tension bar techniques

Kolsky tension bar techniques were modified for dynamic high-temperature tensile characterization of thin-sheet alloys. An induction coil heater was used to heat the specimen while a cooling system was applied to keep the bars at room temperature during heating. A preload system was developed to generate a small pretension load in the bar system during heating in order to compensate for the effect of thermal expansion generated in the high-temperature tensile specimen. A laser system was applied to directly measure the displacements at both ends of the tensile specimen in order to calculate the strain in the specimen. A pair of high-sensitivity semiconductor strain gages was used to measure the weak transmitted force due to the low flow stress in the thin specimen at elevated temperatures. As an example, the high-temperature Kolsky tension bar was used to characterize a DOP-26 iridium alloy in high-strain-rate tension at 860 s −1 /1030 ∘ C.

Research on the Mechanical Response of a Bolt Connection by Experimental and Numerical Method

For a mouth shaped strucure with bolt connection, the mechanical response and thread stress distribution were studied by experimental and numerical method. The structure was tested with variety of the pretension loads from 10 N.m to 70 N.m . In this paper, a numerical method modeling the helical thread was proposed. In the method, the structure was divided into three regions, thread region, conventional region and transition region. The conventional region was modeled with the conventional method, however, the thread region and the transition region were modeled using the Glide-Guide method. Firstly, two helical lines and the plane elements were created. Secondly, the plane elements were rotated along the lines, then the three dimensional elements for the helical model were obtained. Finally, the nodes of the transition region elements and the conventional region elements were merged so that the whole model was attained. The experimental structure was modeled by the method, and the mechanical response and thread stress distribution were obtained. The results show that the axial stress of the screw obtained by experiment and the numerical method were very close, and they were both close to the empirical formula when the equivalent friction coefficient was 0.22 . Comparing to the existing methods, the numerical method proposed in the article is mush simpler, and it can obtain reasonable results using all standard elements.

Fretting fatigue mechanism of bearing cap bolted joints.

Fretting fatigue is a common type of failure of the bearing cap bolted joints. This paper proposes a methodology to analyze the fretting fatigue mechanism of the bearing cap bolted joint. A biaxially loading system was designed to simulate fretting fatigue failure under typical engine working condition. Meanwhile, a submodel was developed in the finite element calculation to analyze the contact status and stress distribution of the structural models. The test result shows that long inclined cracks (about 650 μm long, orientation at 17°-34°) initiate at the middle region of the contact interface. As the increase of the bolt pretension load (from 6000 N to 10,000 N), the crack initial location is getting away from the bolt screw, and the fretting fatigue lives is increasing (from 7.8 × 10(5) to 6.0 × 10(6)). With the fatigue phenomenon and the stress field analysis result, it concludes that the crack initiation is governed by the maximum shear stress; the bolt pretension load and the additional rotate torque caused by the bearing load are the two main factors which affect the fretting fatigue mechanism of the bearing cap bolted joints. It is beneficial to fretting fatigue lives of the bearing cap joints by increasing the bolt pretension load and restraining the oscillation of the bearing cap.

Stress Analysis for Electric Stop Valve of Nuclear Power Plant Considering Action of Preload and Stem Force

The finite element model of electric stop valve with flange bolts preload and valve stem force was established to improve the valve stress calculation method which was based only on action of fluid pressure, thermal stresses and pipe reaction forces. The principle and application of pretension load elements were expounded. By ANSYS, the stresses of this valve with preload and valve stem force were calculated, and the Mises equivalent stresses contour and some values of key position of whole valve were obtained. The results indicate the influence of the stresses on the valve caused by preload of bolt mounted on the flange and valve stem force can not be ignored.

A study on size optimization of rocket motor case using the modified 2D axisymmetric finite element model

In this study, we evaluated the structural integrity and weight of a rocket motor with a torispherical dome by size optimal design. Size optimal design was achieved by first-order and sub-problem methods, using the Ansys Parametric Design Language (APDL). For rapid design verification, a modified 2D axisymmetric finite-element model was used, and the bolt pre-tension load was expressed as function of the ratio of the cross-sectional area. The thickness of the dome and the cylindrical part of the rocket motor were selected as the design parameters. Our results showed that the weight and structural integrity of the rocket motor at the initial design stage could be determined more rapidly and accurately with the modified 2D axisymmetric finite-element model than with the 3D finite-element model. Further, the weight of the rocket motor could be saved to maximum of 17.6% within safety limit.

Three-dimensional interaction between anchor chain and seabed

Following the suction anchor installation, preloading of the anchor chain has to be carried out to remove slack. The assessment of a pretension level should take into account not only the additional chain slippage that may occur in service, but also the chain tension at the pad-eye which is transferred from the touchdown point (TDP) at the seabed. In this paper, a novel quasi-static model, which has considered the three-dimensional (3D) characteristics of soil resistance and chain elastic elongation, is presented to provide an accurate prediction of the behavior of an embedded chain. Based on this model, the chain profiles and tension distributions under different pretension levels are first calculated. While experiencing larger environment loads in service, the embedded chain will produce further movement in 3D space, which can be obtained by taking the chain equilibrium after pretensioning as the initial condition. Finally, the influence of pretension loads and angles at the TDP on the behaviors of embedded chain are thoroughly studied, and some useful conclusions are drawn.

Research on the Pretension of the NGW Reducer Tumbler Bearing

The pretension of the central gear floating NGW planetary gear reducer tumbler bearing is studied. The relative displacements of the inner and outer rings of the tumbler bearing are analyzed according to the light, medium and heavy pretension loads. The tumbler bearing is tested in the different pretension loads. In some operating conditions such as constant power, constant rotating speed and constant torque, etc., the transmission efficiency, vibration and temperature of the reducer are tested and analyzed and the dynamic characteristic curve is obtained. According to the test curve, the principles of choosing the pretension loads of the tumbler bearing are presented. The experiment of this paper is also of reference value for studying the pretension of the other types of reducer bearings.

Numerical investigation of the response of expansion anchors used to attach helical pile connectors to concrete foundations

This paper evaluates the performance of expansion anchors used to attach helical pile connectors to foundations. The anchors’ response to pullout loads was evaluated using nonlinear finite element analysis with the aid of the commercial software, Abaqus. The connector capacity under horizontal movement of the foundation for different anchor diameters, embedment depths, and anchors’ spacing is reported. It was found that the pre-tension load had no influence on the anchor ultimate capacity, but affected the anchor response at service load levels and the displacement at failure. Under pullout loading, increasing the anchor diameter resulted in a more brittle response, but did not affect the ultimate capacity when the concrete tensile strength dominated the response. No interaction between anchors was observed for spacing ≥ 1.67 times the anchor’s embedment depth. A modification to the helical pile connector configuration is proposed.

토리구형 돔 형상을 갖는 연소관의 치수 최적화 설계 연구

본 연구에서는 토리구형 돔 형상을 갖는 연소관의 치수 최적화를 통한 경량화와 구조 안전성을 평가하였다. 치수최적화 설계는 빠른 설계 검증을 위하여 볼트의 단면적 비가 고려된 2차원 축대칭 유한요소 모델을 이용하여 수행하였다. 이때, 해석 프로그램은 ANSYS APDL(Ansys Parameter Design Language)을 이용하였고, 해석법은 sub-problem법과 first-order법을 선택하여 수행하였다. 설계 변수로는 연소관의 돔과 실린더 부위의 두께를 선정하였다. 수정된 2차원 축대칭 유한요소 모델은 3차원 유한요소 모델과의 결과 비교를 통하여 신뢰성을 확인하였고, 초기설계 단계에서 수정된 2차원 축대칭 유한요소 모델을 이용하여 연소관의 구조 안전성 평가와 빠르고 정확한 경량화 설계를 수행할 수 있었다. 연소관의 안전계수에 따른 최적화 해석 결과 최대 17.6%의 무게 절감 효과를 확인하였다.

Experimental and 3D Numerical Simulation of Reinforced Shear Joints

The load transfer capacity and failure mechanism of a fully grouted bolt installed across a joint in shear is investigated, both experimentally and numerically, in five types of bolt. The double-shearing testing of bolts were studied in concrete blocks of 20, 40 and 100 MPa strengths, subjected to different pretension loads of 0, 5, 10, 20, 50 and 80 KN, respectively. The parameters examined include: shear resistance, shear displacement, induced strains and stresses during the bolt-bending process, and its ultimate failure across the sheared joint planes. The conclusions drawn from the study were that the strength of the concrete, bolt profile configuration and bolt pretension load played a significant influence on the shear resistance, shear displacement and failure mechanism of the reinforced medium. Experimental and numerical simulations showed that the failure occurs as a result of the induced axial and shear stresses acting between the hinge point distances in the vicinity of the shear joint plane.

Analytical approach for the design of active grouted rockbolts in tunnel stability based on convergence-confinement method

Assuming that grouted rockbolts increase internal pressure within a broken rock mass, a new procedure for computation of ground response curves for a tunnel reinforced with active grouted rockbolts is presented, while the effect of distance of bolted section to tunnel face has been also considered. This analytical solution for a circular underground excavation under hydrostatic stress field, and with consideration of a non-linear strength criterion for rock mass and on the basis of two material behavior models has been developed. In this work, the equation of the ground response curve for a tunnel which has been reinforced with passive grouted rockbolts is also derived. The proposed model allows one to take, the effect of the distance of the bolted section to the tunnel face, the effect of increasing rockbolts spacing, the influence of increasing pretension load in calculating of the ground response curve, and the effect of increasing the cross-section area of rockbolts, into account. The results show that decreasing rockbolts spacing increase the support system stiffness rather than preloading of them.

Modelling and optimization of sails

The aim of this paper is to improve the quality and the performances of sails by using non-linear modelling, numerical experimentation and optimization methods. The sail is represented by a triangular structure made of composite materials (unidirectional or woven composite) well modelled by an orthotropic membrane behaviour. Under the wind pressure, the sail is submitted to large displacements and small strains. Initial pre-tension load which ensures that the surface is reasonably free of wrinkles is required. The numerical solution is carried out by means of a modified Newton–Raphson method. The mathematical problem of optimization relates to the displacement in the transverse direction of the sail. The parameter of design is the fiber orientation. The optimization method uses the Nelder–Mead algorithm, efficient to solve non-linear problems. The numerical data provided by the sail makers will ensure a comparison between the obtained results and the empirical techniques used by the sail designers.

Solar Sail Topology Variations Due to On-Orbit Thermal Effects

The objective of this research was to predict the influence of non-uniform temperature distribution on solar sail topology and the effect of such topology variations on sail performance (thrust, torque). Specifically considered were the thermal effects due to onorbit attitude control maneuvers. Such maneuvers are expected to advance the sail to a position off-normal to the sun by as much as 35 degrees; a solar sail initially deformed by typical pre-tension and solar pressure loads may suffer significant thermally induced strains due to the non-uniform heating caused by these maneuvers. This on-orbit scenario was investigated through development of an automated analytical shape model that iterates many times between sail shape and sail temperature distribution before converging on a final coupled thermal structural affected sail topology. This model utilizes a validated geometrically non-linear finite element model and a thermal radiation subroutine. It was discovered that temperature gradients were deterministic for the off-normal solar angle cases as were thermally induced strains. Performance effects were found to be moderately significant but not as large as initially suspected. A roll torque was detected, and the sail center of pressure shifted by a distance that may influence on-orbit sail control stability.

Pre-tensioning of fabrics in cement-based composites

This paper studies the effects induced by applying a pre-tension load during the production of fabric–cement composites. The flexural behavior as well as the bonding between the different fabrics and the cement matrix was examined, as a means for characterizing the processing parameters. Microstructure characteristics of the fabric–matrix interface as well as the viscous elasticity properties of the fabrics were also explored and correlated with the mechanical properties of the composite. It was found that pre-tensioning of fabrics and the time at which the tension is removed can significantly influence the performance of the composite depending on yarn properties, mainly the viscous–elastic properties, and fabric geometry.