Nonlinear Performance of Explicit Pseudodynamic Algorithms

A previously published explicit method has been proved to have the same numerical properties as those of constant average acceleration method for linear elastic systems. Although its application to the pseudodynamic testing of nonlinear systems with high frequency modes has been conducted and thus unconditional stability for nonlinear systems was indicated, there is still lack of an analytical proof. In order to explore the nonlinear performance of this explicit pseudodynamic algorithm, a new parameter of instantaneous degree of nonlinearity is introduced to monitor the stiffness change between the stiffness at the end of a time step and the initial stiffness. This parameter enables basic analysis and error propagation analysis for a nonlinear system. In addition, it can also be applied to construct the rough guidelines to select an appropriate time step to conduct a pseudodynamic test although it is almost impossible to achieve this goal using the currently available techniques for a nonlinear system. Analytical results reveal that this algorithm can have unconditional stability for instantaneous stiffness softening and linear elastic systems while it has conditional stability for instantaneous stiffness hardening systems. The proposed rough guidelines for selecting a time step to yield a reliable pseudodynamic test are confirmed with numerical examples.     

Point-to-Surface Pounding of Highway Bridges with Deck Rotation Subjected to Bi-Directional Earthquake Excitations

Post-earthquake survey of several strong earthquakes demonstrated that pounding between the neighboring civil infrastructures, such as building and highway bridge, would induce significant structural damage, even collapse, of the structures. This article presents a pounding experiment of highway bridge, especially focused on the point-to-surface pounding of bridge decks due to torsional rotation, when subjected to extreme bi-directional earthquake excitations. To experimentally investigate the point-to-surface pounding between the neighboring bridge segments, a base-isolated highway bridge model, in which the mass centers of the bridge decks do not strictly coincide with the corresponding stiffness centers, is manufactured. A series of shaking table tests of the highway bridge model are carried out for the structural model with large and small separations of the expansion joint to investigate the dynamic responses of the bridge model with and without including the pounding effects, respectively. An analytical model of the highway bridge, in which the point-to-surface pounding is represented by using a modified contact-friction element, is also established based on the lump mass model with three degrees of freedom for each segment. Based on the test results, the model parameters of the modified contact-friction element are identified, and the analytical responses of the highway bridge model with pounding effects are compared with the experimental data. The results show that the highway bridge is vulnerable to the deck rotation, and point-to-surface pounding should be considered in the structural design to lighten the pounding damage of the highway bridge under strong earthquake excitations.     

Quasi-Static Cyclic Tests of Two U-Shaped Reinforced Concrete Walls

U-shaped or channel-shaped walls are frequently used as lateral strength providing members in reinforced concrete (RC) buildings since their form does not only provide strength and stiffness in any horizontal direction but is also well suited to accommodate elevator shafts or staircases. Despite this popularity, experimental results on the seismic behavior of U-shaped walls are scarce. For this reason a research program with the objective to provide additional experimental evidence for such walls under seismic loading was developed. It included quasi-static cyclic testing of two U-shaped walls at the structural engineering laboratories of the ETH Zurich. The walls were built at half-scale and designed for high ductility. The main difference between the two walls was their wall thickness. The project was chiefly focusing on the bending behavior in different directions and therefore the walls were subjected to a bi-directional loading regime. This article discusses the design of the test units, the test setup and the test predictions. Finally the main results are summarized in terms of failure mechanisms and force-displacement hystereses.     

Effect of SMA Braces in a Steel Frame Building

Pull-back and shaking table test results on a simple model of a three-storey structure that includes shape memory alloys (SMA) copper-based dampers are presented and discussed. The model corresponds to a rigid-framed steel structure and the dampers to austenite CuAlBe wires inserted as bracing at each story. The inclusion of the dissipators in the structure increases the percentage of critical damping from 0.59% for the bare case to 5.95% for the braced system. At the same time, the structural stiffness increases making the first fundamental frequency change from 2.5–3.7 Hz (0.4–0.27s). The net effect of these two factors is a 30–60% reduction of peak relative displacements compared to the ones obtained without dissipation devices when the structure is subjected to earthquake records. Depending on records frequency contents, a reduction of the peak accelerations to near 58% also can be obtained. Additionally, a crude nonlinear analytical model has been studied that can predict the earthquake responses reasonably well.     

HIGHWAY INFRASTRUCTURE INVESTMENT AND COUNTY EMPLOYMENT GROWTH: A DYNAMIC PANEL REGRESSION ANALYSIS*

ABSTRACT This paper uses recent advances in dynamic panel econometrics to examine the impact of highway infrastructure on aggregate county‐level employment using data for all 100 North Carolina counties from 1985 through 1997. Results are compared to models that do not take endogeneity of highway investment and dynamics of employment adjustment into account. Fully specified dynamic models are found to give insignificant results compared to these other models. Thus, when these issues are properly modeled, the results show that improvements in highways have no discernible impact on employment.     

Lightly Reinforced Walls Subjected to Seismic Excitations: Interpretation of CAMUS 2000–1 and 2000–2 Dynamic Tests

In this article a study is presented of the inelastic seismic performance of two 5-story reinforced concrete wall specimens, which were tested in the context of the CAMUS 2000 program. The structure has been sized and detailed following the French PS92 code. To investigate the simplifying assumptions made in design, a 3-D refined nonlinear analysis was conducted. Particular aspects of the behavior of the two tested specimens are presented and then test results are compared with numerical predictions. The experimental-analytical comparisons not only demonstrate the accuracy of the time-history analysis model, but also allow obtaining more detailed information about the behavior of the specimen when it is subjected to seismic excitation. The significant effect of degradation of the stiffness and strength of the wall suggests that it is always important that design procedures are derived from numerical modeling and experimental observations.     

DYNAMIC RESPONSE OF SKEW HIGHWAY BRIDGES

A simplified bridge model suitable for use in a parametric study of short-span skew highway bridges and bridges with stiffness eccentricity is presented. The proposed model is simple, yet it captures all essential features that affect the dynamic response of these bridges. Using this simplified model, formulas for computing earthquake response of the bridges are developed and parameters that significantly influence the dynamic response of the bridges are identified. The study indicates that the response of a given skew bridge depends not only on its deck aspect ratio, the stiffness eccentricity ratio, the skew angles, its natural frequencies, but also on the frequency ratio. In particular, the rotational to translational frequency ratio has a pronounced influence on the dynamic response of the bridge. It is found that skew bridges with high rotational to translational frequency ratios often exhibit less dependence on such parameters as deck aspect ratios, stiffness eccentricity ratios and skew angles.     

Cyclic Response of Non-ductile RC Frame with Steel Fibers at Beam-Column Joints and Plastic Hinge Regions

An experimental study has been conducted on a reduced-scale gravity-load designed test frame to investigate its overall performance due to the addition of steel fiber-reinforced concrete (SFRC) at the critical regions. Two geometrically similar specimens, namely, reinforced concrete (RC) and SFRC, are tested under slow-cyclic lateral loading. End-hooked steel fibers (aspect ratio = 80) of 1.0% volume fraction were used in the SFRC mix for a distance of one-and-half times the member size near the joint regions. The addition of steel fibers improved the damage tolerance, lateral load resisting capacity, lateral stiffness, ductility, and energy dissipation of the frame.     

“路学”视角下公路交通对旅游地的影响维度与机制研究

“路学”是关于道路功能、时空演化及其区域影响的理论,为研究公路交通对旅游地影响提供新视角。借鉴“路学”构建“公路建设及其作用-公路对旅游地的影响-公路与旅游地交互响应”结构模型。结果表明：公路交通对旅游地的影响表现在经济、社会、文化和生态等维度,且具有正向影响。公路在增强旅游地通达性、刺激经济发展和改变生态环境的同时,也具有鲜明的社会文化特性,改变着人们的旅游经历与体验方式,引发地方重构和社会重塑。经济和生态维度对交旅响应有着正向影响,社会和文化维度影响不显著,交旅交互响应对公路交通建设影响不显著。进而基于生产、使用、建构和消费构建影响机制,以期为促进交旅协调发展提供新的理论视角和科学依据。     

Assessing the macrofracture method for identifying Stone Age hunting weaponry

Macrofracture analysis is an experimentally derived method used as an initial step in investigating the hunting function of stone artefacts. Diagnostic impact fractures, which can only develop as a result of longitudinal impact, underpin this method. Macrofracture analysis recently gained favour in Middle Stone Age studies, supporting hypotheses for effective hunting during the late Pleistocene in southern Africa. However, the factors affecting diagnostic impact fracture formation and the interpretation of these fracture frequencies are not yet fully understood. This paper outlines a set of experiments designed to test macrofracture formation under human and cattle trampling and knapping conditions. The results show that: (a) macrofractures occur frequently when stone artefacts are trampled by cattle and humans and in knapping debris; (b) diagnostic impact fractures occur on some of the trampled flakes and knapping debris (≤3%), but significantly less often than in previous hunting experiments; (c) when they do occur, they are likely produced by longitudinal forces similar to those experienced during hunting; (d) considering artefact morphology is important during macrofracture analysis; and (e) macrofracture analysis is not a standalone method, but is most useful as part of a multi-analytical approach to functional analysis. These experiments help to establish a significant baseline diagnostic impact fracture frequency for the interpretation of archaeological macrofracture frequencies.     

Experimental Study on Seismic Performance of Through-Tenon Joints with Looseness in Ancient Timber Structures

ABSTRACT

In order to study the influence of looseness on seismic performance of through-tenon joints, six through-tenon joints specimens in 1:3.2 scale, including one tight-fitted joint and five loose joints, were fabricated according to the Engineering Fabrication Methods of Qing dynasty. The failure modes, mechanical behaviors such as the hysteresis and envelope curves, strength and stiffness degradations, energy dissipation, and deformation of the specimens under low cyclic reversed loading tests were analyzed. Results show that the failure modes of theses joints under positive and negative loadings are bending damage on the big tenon head and tearing damage on the variable cross-section, respectively. The hysteresis curves of joints appear to be anti-Z shape and present typical pinching effect. The greater the degree of looseness is, the more obvious the slippage is. The bending moment, stiffness and energy dissipation of loose joints are lower than those of the tight-fitted joint under the same rotation angle, and the increase in the loose degree cause them to gradually decrease. Meanwhile, the behavior of the through-tenon joints is further simulated by the nonlinear finite element analysis program, and the test results agree well with the numerical analysis results.     

The Effect of Stiffened Floor and Roof Diaphragms on the Experimental Seismic Response of a Full-Scale Unreinforced Stone Masonry Building

An extensive experimental program was carried out at EUCENTRE, within a research project on the evaluation and reduction of the seismic vulnerability of stone masonry structures. The main part of the experimental program has been devoted to the shaking table tests on three full-scale, two-story, single-room prototype buildings made of undressed double-leaf stone masonry. The first building tested was representative of existing unreinforced stone masonry structures with flexible wooden diaphragms, without any specific anti-seismic design nor detailing. In the second and third buildings, strengthening interventions were simulated on structures theoretically identical to the first one, improving wall-to-floor and wall-to-roof connections and increasing diaphragm stiffness. In particular, in the third specimen, steel and r.c. ring beams were used to improve the diaphragm connection to the walls and collaborating r.c. slab and multi-layer plywood panels were used to stiffen floor and roof diaphragms, respectively. This article describes the strengthening interventions applied to the third building prototype and presents the experimental results obtained during the shaking table tests. The results obtained permitted the calibration of a macroelement model representative of the nonlinear behavior of the structure.     

Assessment of Effects of Reductions of Lateral Stiffness along Height on Buildings Modeled as Elastic Cantilever Shear Beams

A simplified model useful for assessing economic losses due to moderate seismicity events in urban areas has been developed by studying the behavior of buildings before yielding their structural system, allowing for nonuniform stiffness along their height. In particular, buildings are modeled as cantilever shear beams with uniform mass and parabolic reduction of lateral stiffness. This particular stiffness distribution is relevant, as it could be expected to occur in buildings where earthquake action is a critical structural design criterion. The equation of motion governing the dynamic behavior of the proposed model is solved analytically, finding mode shapes in terms of first and second zero-order Legendre functions. The solution is verified by comparing it with results obtained from fine mesh finite element models. The effect of reducing the lateral stiffness is then studied in the first five modes of vibration. Results include modal periods, mode shapes, modal participation factors, and derivatives of mode shapes. In general, it is found that effects of reduction of lateral stiffness in mode shapes are moderate when the lateral stiffness in the free end is smaller than about seventy percent of the lateral stiffness at the fixed end, but become significant for larger reductions. Effects are particularly important for the derivative of the mode shapes, which could play a significant role in estimating interstory drift demands in buildings. Model usefulness is showcased by analyzing a test case where both acceleration and drift demands are assessed by considering uniform beams and beams with parabolic stiffness variation, finding notable improvements by considering the latter.     

Wetland assessment and impact mitigation decision support framework for linear development projects: The Louis Riel Trail,Highway 11 North project,Saskatchewan, Canada

Next to agriculture, road development is one of the most significant sources of stress to wetlands in Prairie Canada. However, there currently exists limited guidance for incorporating direct, indirect, and induced effects to wetlands in impact assessment and mitigation planning for small and often routine developments, including access roads or highway improvement initiatives. Based on the Louis Riel Trail, Highway 11 North twinning project in Saskatchewan, Canada, this article demonstrates a methodological approach and decision support framework for assessing and managing direct, indirect, and induced effects to wetlands from linear developments. No regulatory‐based environmental assessment was required for the highway project; effects were deemed to be insignificant under current wetland mitigation practices. However, our results show that 1115 ha of potentially affected wetlands are located within a 500 m impact zone on either side of the proposed highway. More than 50 percent of these wetlands are seasonal, less than 1 ha in size, and typically not included in mitigation planning. An expert‐based multi‐criteria evaluation of impact and mitigation options for wetlands in the study area indicated “no net loss” as a planning priority, and a preference for a spatially ambitious mitigation plan focused on direct, indirect, and potentially induced impacts. In practice, however, mitigation is often restrictive, focused on mitigating only direct impacts within the project's right‐of‐way, in this case less than 50 ha of wetlands, resulting in the potential for significant net loss of wetland habitat and function. If the risk to wetlands is to be given due consideration in project planning and development for roads and road improvement initiatives, then structured assessment methods and decision support frameworks should be sensitive to the time and resource constraints of small projects and screening‐type assessments. This requires also that wetland mitigation policies are developed and implementation plans formulated as part of project planning and assessment initiatives for linear developments.     

Modeling and Prediction of Long-Distance Traffic Flows Through the Example of Road Transport in the Czech Republic

The construction of large-scale long-distance roads brings an irreversible impact on the landscape and therefore its careful and precise planning is very important. For this planning we use data on the intensity of traffic flows on existing roads and statistical tools for the modeling of planned traffic flows. The main objective of this paper is the modeling of the existing intensity of traffic flows on highways and expressways in the Czech Republic by determination of the optimal distance-decay function. On the basis of the resulting model and the resulting distance-decay function, it is possible to predict the intensity of traffic in the event of the completion and commissioning of new sections of highways and expressways. The subsequent analysis will allow us to make a qualified prediction of traffic intensity in the event of the completion of the R35 expressway, or after the completion of the R35 and R43 expressways. Besides the intensity on the above-mentioned roads themselves, the paper also predicts the expected reduction in traffic intensity on the busiest highway in the Czech Republic, that is, on the D1 highway between Prague and Brno.     

莫高窟壁画地仗试件物理力学性能分析

深入了解壁画地仗的物理力学性能,对以后开展壁画的保护工作具有非常重要的意义。为此,通过一系列的测试和试验研究,对莫高窟壁画地仗材料试块开展了物理力学性能分析。测试和试验项目包括块体密度测试、声波波速测试、单轴抗压试验、劈裂法抗拉试验和直剪试验等。通过测试,分别得到了粗泥层和细泥层的密度、纵波波速、横波波速、动泊松比、抗压强度、弹性模量、抗拉强度、粘聚力和内摩擦角等9种物理力学性能参数。本研究成果将为莫高窟壁画的后续保护和修复工程技术研究奠定基础。     

Pseudo Dynamic Testing of an RC Frame Retrofitted with Chevron Braces

Two-story three-bay reinforced concrete frames with and without chevron brace was tested using pseudo dynamic test method. The chevron braces were implemented to the interior span of the RC frame. Chevron-braced frame was observed to be effective to control inter-story drift demands. Based on the observed damage state and dynamic response of the test frames, performance states were discussed for different scales of Duzce ground motions. The test results were compared with the results of the nonlinear time history analysis. The analysis results were capable of estimating the base shear capacity and displacement demands with a reasonable accuracy.     

Cyclic Response of Concrete Beams Reinforced by Plain Bars

There are many reinforced concrete structures throughout the world that have been built in the past decades that lack appropriate seismic details and reinforced by plain bars. To study the behavior of such buildings, seven beams have been tested under cyclic and monotonic load. The specimens include substandard specimens, with deficient seismic details and reinforced by plain bars, specimens designed in accordance with ACI-318-99 but reinforced by plain bars, and standard specimens reinforced by deformed bars. The tests indicate that the substandard specimens sustain relatively large slip of longitudinal bars, separation of specimen relative to foundation and sliding at large deformation phase, low initial stiffness ratio, limited lateral displacement capacity, and loss of nominal yield strength. The specimens reinforced by plain bars in accordance with ACI-318-99 perform almost similar to standard specimens with deformed bars, in terms of elastic stiffness and lateral displacement ductility; but, they sustain larger slip, and smaller yield strength. Failure of all specimens reinforced by plain bars is characterized by flexural cracks without visible shear failure. Residual shear strength of substandard specimens is modeled by dowel action of longitudinal bars to predict a lower limit for lateral strength of the specimens.     

A Base Isolation System for Developing Countries Using Discarded Tyres Filled with Elastomeric Recycled Materials

This article studies the performance of economic base isolators using tyres filled with elastomeric recycled materials. The research was conducted to analyze base isolators to be used in developing nations, where the application of conventional elastomeric rubber bearings due to economic reasons is limited.

The tested isolators are made of kart tyres filled with different recycled elastomeric materials and aggregates. Dynamic and static tests proved acceptable vertical to horizontal stiffness ratio of the bearings and shake table tests showed an excellent enhancement of the base isolated structural response compared to the corresponding fixed base structure.     

Planning Analysis and Political Steering with New Public Management

Interviews with members of the Norwegian national assembly's Standing Committee for Transport and Communications were conducted in 1995, 1997, 2001 and 2004. The politicians were asked about the usefulness of analytic input that planners contribute to national plans, first the Norwegian Road and Road Traffic Plan and later the National Transport Plan. Questions related to steering, coordination, delegation and the inclusiveness of the planning process were also posed. Changes in the politicians' attitudes to types of analytic planning input are outlined. Furthermore, the last round of interviews sheds light on the apparent paradox that parliamentarians accept delegation of highway investment decisions despite their profound scepticism regarding the cost–benefit analyses and impact calculations that are essential to management by objectives and results (MBOR), which was to give them continued political control despite delegation. Another conundrum is the parliamentarians' willingness to renounce the right to decide over most highway projects, even if these were seen as politically important, in order to obtain a strategic overview which they have been unable to use for changing the priorities set by the Government. The political concentration on strategic steering, the concomitant delegation, and MBOR are central components of New Public Management.