金川二矿区不良岩层巷道地压活动规律及控制方法的研究

本文从理论和实践的结合上阐述了不良岩层巷道维护问题。其要点是:①找出了1978年以前金川在不良岩层中采用多种支护型式都难以维护的根本原因是:把流变体围岩稳定问题视为单纯的传统支护结构问题;②确定了不良岩层的基本属性为易发展为松散体的流变体,从理论上阐明了不良岩层巷道必须分次支护的理由;③查明了不良岩层巷道地压类型,以流变体变形地压为主;④总结了地压活动基本规律,分析了在围岩纵深12米范围内,最终出现的二个压密区、一个松驰区、一个松动区,压密区实际上是承载环,在围岩稳定过程中起着关键作用,从理论上解释了金川不良岩层巷道围岩稳定过程;⑤采用了信息化设计——现场监控设计法;⑥提出了金川不良岩层巷道支护原理和设计方法,即根据岩层不同属性,不同地压来源,从分析地压活动规律入手,运用信息化设计法,使支护特性和施工工艺过程不断适应围岩变形的活动状态,以达到抑制围岩变形、维护巷道稳定的目的。     

Structural Analyses and Assessment of Historical Kamanl? Mosque in Izmir, Turkey

Historical structures are one of the most precious pieces of cultural accumulation. In this study, an interdisciplinary work was conducted to assess the structural condition of a historical masonry structure, Urla Kamanl? Mosque in ?zmir, Turkey. The structure is a member of group of structures, Yah?i Bey Complex, which includes a Turkish bath, a tomb, two fountains, and a primary school. The structure dates back to early 14th century to mid-15th century. History investigation, measurement survey, long-term settlement, and moisture observations were conducted. Nondestructive and destructive material tests were performed on stone, brick, and mortar. 3D finite-element model of the structure was used to investigate the critical locations of the structure under its self-weight, seismic load, and settlement load. Linear elastic and nonlinear settlement analyses were conducted to investigate the reason for massive cracks challenging the structural integrity.     

Static Load Tests of a Road Bridge with a Flexible Structure Made from Super Cor Type Steel Corrugated Plates

The way in which a new road bridge made from Super Cor steel plates was tested is described and the test results for three static load schemes in which one ballasting vehicle (a Scania truck) was used as the load are presented. The tested bridge has a box structure and it is located on the Gim?n River in Gim?n, Sweden on the Br?cke-Holm road. The bridge has an effective span of 12.315?m and a clear height of 3.555?m. The span’s steel shell is founded on two reinforced concrete continuous footings. The average measured displacements and strains (normal stresses) in selected points and elements of the steel shell structure were found to be much smaller than the ones calculated for the same load. The conclusions drawn from this research can be useful for assessing the performance of such steel shells and their interaction with the surrounding backfill. Since such steel–soil designs are used more and more often for small and medium-sized bridges on road and railway lines in Poland and in the world, the conclusions from the static load tests can be generalized to a whole class of similar bridge designs.     

Load Proportion Factors for Metal Railing Systems

Computer models of 20 metal railing systems were created and analyzed to determine the lateral distribution of load and the sharing of load between posts in a multispan rail system. Single rail, double rail, triple rail, and picket rail pipe railing systems with two and four continuous spans of 0.9144?m (36?in.), 1.2192?m (48?in.), 1.524?m (60?in.), or 1.8288?m (72?in.) were considered. The resulting distribution of load between the adjacent posts was compared to the design nomograph that currently defines the practice. Trend line equations extracted from this data showed that the different railing types produced varied degrees of load sharing under the same loading conditions. Recommendations for load proportion factors that differ from the current recommendations are provided.     

Punching Shear Behavior of Flat Slabs Strengthened with Fiber Reinforced Polymer Laminates

The present work reports the test results of seven full-scale reinforced concrete slab-column edge connections strengthened against punching shear using different methods. In this study, three slabs contained openings in the vicinity of the column, and the other four were without openings. The dimensions of the slabs were 1,540×1,020×120 mm with square columns (250×250 mm). The openings in the specimens were square (150×150 mm) with the sides parallel to the sides of the column. The slabs were reinforced with an average reinforcement ratio of 0.75%. Except for the two reference slabs, two different strengthening techniques were considered. Technique I applies externally bonded fiber reinforced polymer (FRP) flexible sheets on the slab around the column in two schemes with one or two layers of FRP sheets glued to the tension face or both tension and compression faces of the slab. Both glass and carbon FRP sheets were considered. Technique II applies externally bonded FRP sheets using either the first or second scheme combined with installing steel bolts through holes across the slab thickness around the column. Based on the test results, it is concluded that the presence of FRP sheets and steel bolts substantially increased the punching capacity of the connections. Code design expressions were conservative in predicting the experimental results.     

Nonlinear Buckling and Postbuckling of Cable-Stiffened Prestressed Domes

Nonlinear buckling phenomenon of a novel type of structure, namely, a prestressed dome, is investigated using a nonlinear finite-element model. A prestressed dome is formed by buckling its individual flat members into arch frame works, and then the structure may be stiffened by cable loops in the circumferential direction. A corotational formulation of a 3D beam element, and a cable element, which is modeled as a catenary between connected points in the dome, are used to develop an algorithm for nonlinear stability analysis of the system by considering large displacements and rotations. The incremental load technique using a Newton-Raphson iteration scheme in conjunction with Crisfield's modified arc-length method is utilized to trace the nonlinear path of equilibrium. Buckling of prestressed domes with different numbers and locations of cable stiffeners are studied, and the results show that skeletal domes with stiffeners buckle at much higher loads than the corresponding unstiffened domes.     

Stress Analysis of Monolithic Circular Arches Strengthened with Composite Materials

This paper presents an analytical approach for the elastic stress analysis of monolithic circular arches strengthened with externally bonded fiber-reinforced polymer (FRP) strips. Emphasis is placed on the interfacial stresses between the existing structure and the supplemental reinforcement layers. Two analytical models are presented: The first model formulates the governing equations in terms of the displacements in the arch and the FRP strip and the tangential distribution of the shear stresses in the adhesive layer as unknowns without involving any assumptions on the stress and displacement fields in the adhesive layer. The second model uses the functional form of the displacement field derived in the first model yielding a formulation in terms of displacement unknowns only. Two numerical examples that examine the capabilities of the analytical approach are discussed. The first example focuses on the stress analysis of a strengthened arch under a localized load. The second example studies the elastic response of a partially strengthened arch to a symmetric load and a horizontal support settlement. The numerical study quantifies the interfacial shear and peeling stresses between the old and the new components underlining the stress concentrations. Finally, conclusions are presented and directions for future research on the application of the theory to masonry arches are outlined.     

Residual stress-affected diffusion during plasma nitriding of tool steels

Plasma nitriding of tool materials is common practice to improve the wear resistance and lifetime of tools. Machining-induced compressive residual stresses in shallow layers of some tenths of microns are observed accompanied by other characteristic properties of machined surfaces in these high-strength materials. After plasma nitriding of M2 high-speed steel, previously induced compressive residual stresses remain stable and the depth of diffusion layers decreases with increasing compressive residual stresses. This article reports investigations of plasma nitrided samples with different levels of residual stresses induced prior to the nitriding process. For comparison, experiments with bending load stresses during plasma nitriding have also been carried out. The plasma nitriding treatment was performed at constant temperature of 500 °C with a gas mixture of 5 vol pct N₂ in hydrogen. Nitriding time was varied from 30 to 120 minutes. All samples were characterized before and after plasma nitriding concerning microstructure, roughness, microhardness, chemical composition, and residual stress states. Experimental results are compared with analytical calculations on (residual) stress effects in diffusion and show a clear effect of residual and load stresses in the diffusion of nitrogen in a high-strength M2 tool steel.     

Mapping the lifetimes of local opening events in a native state protein

The rate constants for the processes that lead to local opening and closing of the structures around hydrogen bonds in native proteins have been determined for most of the secondary structure hydrogen bonds in the four-helix protein acyl coenzyme A binding protein. In an analysis that combines these results with the energies of activation of the opening processes and the stability of the local structures, three groups of residues in the protein structure have been identified. In one group, the structures around the hydrogen bonds have frequent openings, every 600 to 1,500 s, and long lifetimes in the open state, around 1 s. In another group of local structures, the local opening is a very rare event that takes place only every 15 to 60 h. For these the lifetime in the open state is also around 1 s. The majority of local structures have lifetimes between 2,000 and 20,000 s and relatively short lifetimes of the open state in the range between 30 and 400 ms. Mapping of these groups of amides to the tertiary structure shows that the openings of the local structures are not cooperative at native conditions, and they rarely if ever lead to global unfolding. The results suggest a mechanism of hydrogen exchange by progressive local openings.     

Field Load Tests and Numerical Analysis of Qingzhou Cable-Stayed Bridge

A field load test is an essential way to understand the behavior and fundamental characteristics of newly constructed bridges before they are allowed to go into service. The results of field static load tests and numerical analyses on the Qingzhou cable-stayed bridge (605?m central span length) over the Ming River, in Fuzhou, China are presented in the paper. The general test plan, tasks, and the responses measured are described. The level of test loading is about 80–95% of the code-specified serviceability load. The measured results include the deck profile, deck and tower displacements, and stresses of steel-concrete composite deck. A full three-dimensional finite-element model is developed and calibrated to match the measured elevations of the bridge deck. A good agreement is achieved between the experimental and analytical results. It is demonstrated that the initial equilibrium configuration of the bridge plays an important role in the finite-element calculations. Both experimental and analytical results have shown that the bridge is in the elastic state under the planned test loads, which indicates that the bridge has an adequate load-carrying capacity. The calibrated finite-element model that reflects the as-built conditions can be used as a baseline for health monitoring and future maintenance of the bridge.     

Tests During Three Stages of Construction of a Road Bridge with a Flexible Load-Carrying Structure Made of Super Cor Type Steel Corrugated Plates Interacting with Soil

The way in which a new road bridge made of steel corrugated plates Super Cor type was tested during the three stages of its construction is described and the test results are presented. Backfill in construction Stage I and two ballasting vehicles in Stages II and III constituted the loads. The box bridge spans the Bystrzyca Dusznicka River in Polanica Zdroj, Poland. The span’s effective length is 12.27?m and its vertical inside diameter is 3.85?m. The steel span is founded on two reinforced concrete strip foundations. The average values of the displacements and strains (normal stresses) measured in selected points and on selected elements of the steel shell structure were much smaller than the ones computed for the same load. The conclusions drawn from this research can be helpful in determining the interaction between the steel shell and the backfill. Since this type of steel–soil structure is increasingly used in Poland and in the world, the conclusions can be generalized to a whole class of similar bridge designs.     

Behavior of Plate Load Tests on Soil Layers Improved with Cement and Fiber

The load-settlement response from three plate load tests (300 mm diameter, 25.4 mm thick) carried out directly on a homogeneous residual soil stratum, as well as on a layered system formed by two different top layers (300 mm thick)—sand-cement and sand-cement fiber—overlaying the residual soil stratum, is discussed in this technical note. The utilization of a cemented top layer increased bearing capacity, reduced displacement at failure, and changed soil behavior to a noticeable brittle behavior. After maximum load, the bearing capacity dropped towards approximately the same value found for the plate test carried out directly on the residual soil. The addition of fiber to the cemented top layer maintained roughly the same bearing capacity but changed the postfailure behavior to a ductile behavior. A punching failure mechanism was observed in the field for the load test bearing on the sand-cement top layer, with tension cracks being formed from the bottom to the top of the layer. A completely distinct mechanism was observed in the case of the sand-cement-fiber top layer, the failure occurring through the formation of a thick shear band around the border of the plate, which allowed the stresses to spread through a larger area over the residual soil stratum.     

A Polarization Modulation Method for Study Internal Stresses in Composite Ceramics

A polarization modulation method has been used to record internal stresses in composite technique. The optical scheme is presented together with the experimental technique. Internal stresses have been examined around the boundaries of successively joined ceramic layers and at the transition boundary in a two-layer hot-pressed ceramic specimen. The stresses have been determined in the two-layer specimen.     

The early stage of fatigue crack propagation in al 2048

Microcracks which develop at the surface of Al 2048 subjected to fully reversed fatigue loading are found to be partially open at zero load. The magnitude of such residual crack openings measured at the test specimen surface is determined as a function of the crack length and the relative humidity in which the specimens were fatigued. For a fixed crack length the residual crack openings are found to be largest if the relative humidity is low or if the crack path is particularly irregular. The present interpretation of the phenomenon is that the residual crack openings are indirectly related to the crack closure load associated with the microcracks.     

Load Rating and Reliability Analysis of an Aerial Guideway Structure for Condition Assessment

Aerial guideways are elegant transportation structures that are seen at airports, theme parks, and crowded urban areas. The guideways generally consist of continuous, prestressed concrete beam spans, precast concrete columns, and steel beam-column connections. Although there are guidelines prepared as a supplement to conventional highway and railway bridge design codes, aerial guideways form a different class, relatively less studied compared to common highway bridges. The primary objective of this paper is to present a study to better understand the structural behavior and capacity used in an existing guideway structural system which has been in service for about 35?years. The load demand on the guideway system has increased by about 50% over the years. The structural system is composed of six-span continuous prestressed concrete bridge segments. In order to develop models that bound the possible existing condition of the structure, several models are developed by changing the most critical parameters. The critical parameters are categorized as material properties, prestress losses, boundary conditions, and continuity conditions. Sensitivity studies are conducted using eight parametric models for simulations with moving loads for the two different train types. The load rating and reliability indexes are computed for all the cases under different loading conditions. The parameters that have the most influence on the load rating and reliability are also presented. The information generated from these analyses can be utilized for better-focused visual inspection and can also be used for developing a long-term structural monitoring plan.     

The role of backside polishing, cup angle, and polyethylene thickness on the contact stresses in metal-backed acetabular components

Mechanical interactions between the polyethylene liner and the metal-backing play an important role in the load transfer and debris-generation mechanisms of an acetabular component. Insert thickness, cup orientation, and insert-shell interface conditions affect the resulting contact stresses at the articulating and backside surfaces of the polyethylene component. The objective of this study was to determine the variation in contact stresses on a hemispherical acetabular component as a function of the friction coefficient of the line-shell interface, the thickness of the insert, and the load application angle. Three-dimensional finite element models of a metal-backed acetabular component with liner thicknesses of 3-12 mm were developed. The insert-shell interface was modeled as either matte or highly polished, and the load angle of the joint reaction force was changed from 36 to 63 degrees with respect to the dome. We found that the contact stresses at the articulating and backside surfaces of the insert were relatively insensitive to changes in the coefficient of friction at the insert-shell interface (resulting in approximately 1-10% variation in contact stress), when compared to the effect of changing the insert's thickness (approximately 80% variation in contact stress) or changing the direction of the joint reaction force (approximately 20% variation in contact stress). The results of this study suggest that polishing the metal at the insert-shell interface does not substantially change the contact stresses at either surface of the component. Of the design variables available for selective modification by either the surgeon or the engineer, insert thickness and shell orientation play a greater role in determining the magnitude of the resulting contact stresses.     

Residual stress relaxation of welded steel components under cyclic load

It is a well known fact that the fatigue strength and the life of welded steel components are affected, to a considerable extent, by residual stresses distributed around their weldments. When externally applied load is superimposed on residual stresses, unexpected deformations and failure of the components can occur. These residual stresses are not constant, but are relaxed or redistributed during in‐service. Under monotonic load relaxation takes place when the sum of external and residual stress locally exceeds the yield stress of material used. It is noteworthy that under cyclic load the residual stress is considerably relieved by the first or the early cycles of load, and then is gradually relaxed with increasing loading cycles. Although many investigations in this field have been carried out, the phenomenon of and mechanism of stress relaxation are still not clear, and only a few comprehensive models have been proposed to predict amount of relaxed residual stress. In this study, the characteristics of residual stress relaxation under monotonic and cyclic load were investigated, and a model for quantitatively predicting the amount of residual stress relaxation is proposed.     

A comparison of microcrack closure load development for stage I and II cracking events for Al 7075-T651

Closure stress measurements for both Stage I and II surface microcracks of lengths comparable to grain size are made using a compliance technique for Al 7075-T651 specimens fatigued in air at 30 pct relative humidity. As previously reported for Stage II cracking in Al 2219-T851, residual crack openings are observed for zero load which can be empirically related to the crack closure stress. This functional dependence is subsequently used to calculate closure stress values for both Stage I and II events for microcracks in Al 7075-T651 on the basis of residual crack opening values. Stage I crack interaction with grain boundaries is found to induce closure stresses close to the maximum applied stress, explaining the effective crack retardation of Stage I cracks by grain boundaries observed for Al 7075. In these cases the closure load is found to slowly fall as cracking continues by a Stage II mode into a second grain. For Stage n cracking it is possible to estimate the closure load from the cracking path as observed from the surface.     

Turbulent Stresses at the Bottom Surface near an Abutment: Laboratory-Scale Numerical Experiment

The flow field around a bridge abutment is analyzed by means of large eddy simulation. The geometrical configuration corresponds to the initial condition of a scour process (flat bed). The three-dimensional flow structure in front of the abutment is analyzed with special emphasis on its effects on shear stresses and pressure gradients on the bottom wall which, in turn, are discussed with respect to their potential scouring action. Both first- and second-order statistics around the abutment are quantitatively discussed, together with probability density distributions of stresses in specific locations. The investigation shows that several terms may play a relevant role in sediment transport around the obstacle. Specifically, the mean horizontal pressure gradient may reach values as large as two orders of magnitude that of a canonical boundary layer, whereas the instantaneous vertical pressure gradient may give an uplifting force comparable to the immersed weight of the sediment. The analysis suggests that local scour models should incorporate the contribution to the destabilizing force coming from pressure stresses and from turbulent fluctuations.     

Dynamic Characteristics of SDOF Structure with Maxwell Element

Dynamic characteristics are analytically investigated for a single degree of freedom structure with a Maxwell element (SSME). Eigenvalues are obtained analytically and approximated by a perturbation method. Then, cases are sorted by a stiffness ratio λ: the ratio of a structural spring to an auxiliary spring. For a small λ, the optimal damping ?c provides the maximum damping ratio. For a large λ, the lower and upper critical dampings ?a and ?b provide duplex eigenvalues. These values are approximated by simple terms. To reduce transient response, λ should be large, and ? should be around ?c, ?a, and ?b, which provide the SSME with large damping. For a stationary excitation, the optimal damping ?d is introduced to produce the minimum peak deformation. In fact, ?d is larger than ?c and ?b, and provides larger stiffness and a smaller damping ratio. For a seismic excitation, some cases with ?d might reduce deformation more than those with ?c and ?b, but must support larger stress in the Maxwell element. Thus, ? should be based on design constraints.