Current Design Requirements Research Articles

Seismic retrofit of external RC beam–column joints by joint enlargement using prestressed steel angles

Reinforced concrete (RC) structures that were built prior to the 1970s generally do not meet current seismic design requirements, especially in terms of reinforcement details. An innovative and practical seismic retrofit method is proposed for non-seismically detailed external beam–column joints of existing concrete structures, based on a two-dimensional enlargement of the beam–column joint using steel angles that are mounted using prestressed cross-ties. Seven half-scale external RC beam–column joints were subjected to lateral cyclic loading of increasing amplitudes. The tested specimens comprised of three control units and four retrofitted units. The test results confirmed that the proposed retrofit method not only resulted in relocation of beam plastic hinges to outside the joint panel zone but also improved the bond between the longitudinal beam and column tension reinforcement and concrete in the joint panel zone. The proposed method was shown to significantly enhance the seismic capacity of the joints, in terms of strength, stiffness, energy dissipation and ductility capacity.

Design tools for thermoactive geotechnical systems

AbstractThis paper presents a review of current design tools used for thermoactive geotechnical systems, along with validation efforts. The capabilities of available analytical methods used for the thermal and thermomechanical design of these systems are evaluated and shortcomings of the existing methods are identified. Although the analytical methods permit accurate prediction of the thermal stress and strain response of thermoactive piles from readily available soil and concrete properties, current shortcomings consist of the ability of the methods to simulate cyclic heating and cooling effects, transient pore water pressure generation and dissipation, and the effects of radial stress changes. Recommendations are provided on how to properly address the current design requirements and the efforts to overcome shortcomings with the development of constitutive relationships from further full scale and laboratory scale experimental studies on thermoactive piles. Furthermore, the need for the development of b...

HSS-to-HSS seismic moment connection performance and design

Abstract Hollow structural sections (HSS) provide an alternative to typical wide flange sections in low-rise seismic moment resisting frames. Their beneficial strength-to-weight ratio as well as bending, compression, and torsional resistance increases the versatility of moment frames and potentially improves performance under earthquake loads. With an understanding of current design requirements for seismic moment connections and static HSS-to-HSS connections, 39 fully welded unreinforced HSS-to-HSS connections are explored through finite element analyses. However, performance is limited due to column face plastification and inability to develop the plastic moment capacity of the beam. To rectify this problem, 24 through plate and 24 external diaphragm plate HSS-to-HSS moment connections are analyzed. Several important geometric parameters, such as the beam width–column width ratio, beam thickness–column thickness ratio, plate length, and plate thickness are considered to understand their effect on the connection moment capacity and sources of inelastic rotation. The through plate and external diaphragm reinforcement greatly improve the connection behavior moving yielding away from the column face and into the beam member. The results from the reinforced connections are used in combination with current seismic design provisions to develop a design procedure that optimizes the performance of these connections. The reinforced connections can be detailed to develop plastic hinging in the HSS beam member while minimizing the likelihood of a non-ductile weld failure.

Analytical Study on the Structural Behaviors of Stub Columns Fabricated with HSA800 of High Performance Steel Subjected to Eccentric Loads

In this study, the stub columns of built-up H-section and square hollow section subjected to eccentrical loads are tested to evaluate the applicability of the structural members with 800MPa high-strength steel (HSA800) on current design specification. Analytical studies of FE model are conducted to validate the test results and then the verified FE models are used for extensive parametric studies for checking up the applicability of current design code. The parameters are width-to-thickness ratios and axial load ratios. From P-M correlations on parameter models, all stub columns with non-compact sections exceed the current design requirements about axial force and flexural strength ratios are sufficiently secured as the axial load ratios are decreased. The built-up hollow sections with slender section model do not satisfy the current design specification about axial force.

휨강도와 전단강도의 확률분포를 고려한 연결보의 성능기반설계

연구에서는 휨힌지를 유도하기 위해 휨강도와 전단강도의 확률분포를 고려한 연결보의 성능기반설계법을 제안하였다. 이 방법은 연결보의 항복 이후 거동과 시스템의 재분배를 반영하므로 현행 선형해석 기반의 연결보 설계에서 임의로 저감된 유효강성의 적합성을 검증할 수 있으며, 사용하중에서의 연결보의 실제 강성을 반영하여 횡변위를 평가하는데 적정하다. 또한 부재간 내력 재분배를 고려할 수 있어 병렬전단벽의 최적설계가 가능할 것으로 판단된다. 이 설계법의 적합성을 검증하기 위해 단순화된 30층 오피스 건물을 대상으로 비선형정적해석을 수행하고 성능점 및 각 스텝의 구조성능을 검토하였다. 또한 사용 하중의 부재강성을 평가하고 극한하중의 부재 강성을 사용한 시스템의 거동과 비교하였다. 또한 연결보의 다양한 배근 및 보 춤에 따른 시스템의 거동특성을 비교, 분석하였다.<BR>

A Holistic Stray Current Assessment of Bored Tunnel Sections of DC Transit Systems

In considering the stray current design for dc transit systems, the stakeholders should comply with the objective that the stray current design requirement is to minimize the impact of the stray current on the supporting infrastructure and on the third party infrastructure. This paper defines a holistic stray current assessment for bored tunnel sections (BTSs) of dc transit systems, by utilizing a boundary-element platform. The developed method enables the stray current performance of various design options and characteristics to be assessed on the tunnel system. Most important, the methodology proposed offers the means to evaluate the stray current performance of a BTS in terms of its geometry and topology. Finally the postprocessing steps that facilitate the benchmarking of the results against the relevant EN standards are discussed.

Practical Model for Three-Stage Corrosion Behavior of Galvanized Steel Reinforcement in Soil

Failure of mechanically stabilized earth (MSE) walls attributed to the corrosion of galvanized steel in soil has raised concern on the adequacy of current design requirements. In this work, a numerical model was developed to calculate the corrosion rate of galvanized steel in soil at three different stages of corrosion by considering key soil corrosion parameters, such as resistivity, temperature, moisture content, pH, and oxygen availability. Results show that the proposed model is in agreement with widely accepted empirical models, and can be used for the service-life design and risk assessment of MSE walls and to determine the optimum zinc cover thickness.

Risk-Based Strategies for Upgrading Existing Nonconforming Wooden Houses and Risk Information for Promoting Upgrading

There is widespread awareness in seismic-prone countries about the necessity to upgrade the seismic performance of old buildings and wooden houses for disaster mitigation; however, upgrading occurs at a very slow pace. At present, Japan has approximately 11 million nonconforming old wooden houses, but most of them remain without upgrade because of the large expenditure that would be incurred by both house owners and the local government. An owner would need to spend approximately US$11,000 on average to upgrade his/her house such that it satisfies the current design requirements. In Aichi prefecture alone, upgrading would cost approximately US$10 billion in total, which is approximately 40% of the annual budget. This study, therefore, investigates alternative strategies for upgrading existing nonconforming wooden houses more efficiently and cost-effectively. The seismic risks of wooden houses as a whole in Aichi prefecture are estimated, and then the effective target level for upgrading is discussed from the viewpoint of both economic loss and the number of fatalities. It is shown here that it is worthwhile from the viewpoint of life safety to consider a target upgrading level that is lower than the current design requirements. Although the analytical models discussed in this paper might be specific to Japan, the framework of the risk assessment is universal and the conclusions drawn from this analysis are applicable to other seismic-prone regions and countries.

A balanced design procedure for special concentrically braced frame connections

Concentrically braced frames (CBFs) are stiff, strong structures that are suitable for resisting large lateral loads. Special CBFs (SCBF) are used for seismic design and are designed and detailed to sustain relatively large inelastic deformations without significant deterioration in resistance. Current AISC Seismic Design Provisions aim to ensure the brace sustains the required inelastic action, but recent research showed that current SCBF design requirements lead to variable seismic performance, unintended failure modes, and limited deformation capacity. To improve the seismic response of SCBFs, a balanced design procedure was proposed. The premise of the design methodology is to balance the primary yield mechanism, brace buckling and yielding, with other, complementary ductile yielding mechanisms, such as gusset plate yielding. This balance process maximizes ductile yielding in the frame thereby maximizing the drift capacity of the frame. Further, the undesirable failure modes are balanced with the yield mechanisms and the preferred failure mode, brace fracture, to ensure that the frame fails in the desired manner. To achieve the objectives of the design methodology namely maximum drift capacity, and adherence to a desired yield and failure hierarchy, rational resistance checks and appropriate balance factors (β factors) are used to balance each yield mechanism and failure mode. These factors were developed, validated, and refined using the measured results from an extensive test program. An SCBF connection design example to illustrate the application of the balanced design method and to demonstrate differences from the current AISC design method is presented in an appendix.

Pressure treatment of composites in controlled media

The pressure treatment of composites in controlled media is considered within the framework of its history and prospects. Trends in the development of vacuum rolling mills in production lines subject to current design and performance requirements are outlined. New production technologies for high-performance products are described.

Analisa dan Perancangan Jaringan Berbasis VPN Pada PT. Finroll

Along with the development of the company to run operations such as data communication and perform other transactions to relations and vice versa, PT Finroll just uses the public network such as sending email to their partners. Data information is not safe in public because it can be tapped or intercepted by unauthorized person. With the Virtual Private Network (VPN), PT Finroll can do business in secure environment to their partners. The methodologies used in this research are data collection that was started by surveying, interviewing, and analyzing the current network topology, performance and design requirements that support network design. From these results, PT Finroll can increase productivity and performance from competition in their business. In addition, with this research company has a better ability to increase their competitiveness in present and the future.

Behavior of Vertical Boundary Elements in Steel Plate Shear Walls

The AISC Seismic Provisions and CSA S-16 Standard require a minimum moment of inertia for the vertical boundary elements (VBEs) in steel plate shear walls (SPSWs) to avoid undesirable VBE behaviors. The equation limiting VBE flexibility has been derived from a flexibility factor, , developed in plate girder theory and the limit on VBE flexibility has been empirically specified based on previous test results. This paper reviews the derivations of the flexibility factor and how that factor was incorporated into current code design requirements for SPSWs. Then, analytical models to prevent VBE shear yielding and to estimate the out-of-plane buckling strength of VBE are developed, followed by a review of past experimental data to investigate if the significant inward VBE inelastic deformation and out-of-plane buckling observed in some instances were due to excessive VBE flexibilities or other causes such as shear yielding at the ends of the VBEs. It is shown that the existing limit on is uncorrelated to satisfactory in-plane and out-of-plane VBE performance. The proposed analytical models predict performance of previously tested SPSWs that correlates well with the experimental observations.

Seismic Design Strength of Cold-Formed Steel-Framed Shear Walls

A method for estimating the available strength level (load and resistance factor design) seismic resistance of light-frame cold-formed steel shear walls is discussed. The proposed method attempts to account for the early onset of inelastic behavior in light-frame shear walls by evaluating the strength level resistance in terms of an equivalent shear wall yield strength. Application of the proposed method is illustrated using shear wall data from an independent test program and wall performance is compared to current light-frame bearing wall design requirements and expected system performance. It is shown that the proposed method results in design values that are generally conservative compared to current design recommendations and the overall performance of the tested walls is characterized using five parameters that relate common design strength and displacement quantities.

Racking shear resistance of prefabricated straw-bale panels

The present study investigated the resistance to racking shear of 3 m × 3 m low-carbon, high-thermal-performance, prefabricated cladding panels that use straw bales. Although developed as a non-load-bearing panel for use with structurally framed buildings, the panels have the potential for use in low-rise, load-bearing structural walling. Test results confirmed that the panels exceeded current design requirements for racking shear and identified the mechanism whereby this occurred. The panels are considered suitable for future applications in low-rise structural walling solutions. A UK patent application (no. 0803489.4) has been filed on the panel.

Strategies for the management of bridges for vehicular impacts

Impacts on bridges by road vehicles are a relatively frequent occurrence and can lead to delays for road users, injuries or fatalities for vehicle occupants and in some cases risks of major incidents from derailments on railway lines carried by highway bridges. This paper gives an overview of the scale of the problem in the UK taken from data gathered by Network Rail and the Highways Agency (HA). The primary reasons for bridge-deck strikes are given and a review is undertaken of various industry good practice guides and strategies to prevent or deal with these incidents. The background to the development of the current design and assessment requirements is given, including some research and development projects undertaken by the HA. The design requirements from the Eurocode for accidental actions and an outline of risk methodology being developed in the proposed UK national annex to the Eurocode are also presented.

EFFECTIVE STRATEGY FOR UPGRADING WOODEN HOUSES AND RISK INFORMATION FOR ADVANCEMENT OF UPGRADING

There are about 10 million existing non-conforming wooden houses today in Japan, and upgrading the seismic performance of such houses is essential for disaster mitigation. However, most of them remain untouched because of large expenditure for upgrading for both the owners and society. The owners have to spend about 1.1 million yens on average to satisfy the current design requirement. In Aichi prefecture alone, it would cost about one trillion yens, which is more than 1/3 of the annual budget, to upgrade all of them. In order to implement the upgrading of existing non-conforming wooden houses more efficiently, this paper investigates the alternative strategies for upgrading. The seismic risks of wooden houses as a whole in Aichi prefecture is estimated and then the effective target level for upgrading is discussed from the viewpoint of both economic loss and the number of fatalities.

Flexural Strength Design of Concrete Beams Reinforced with High-Strength Steel Bars

Current design requirements limit the allowable design strength of high-strength steel reinforcements to 80 ksi (550 MPa), which limits engineers from fully using the enhanced strength characteristics of low-carbon and chromium high-strength steel. In this paper, a methodology is presented for the flexural strength design of concrete beams reinforced with high-strength reinforcing steel that conforms to the requirements of ASTM A1035-07. The design method is based on simple analysis techniques that satisfy fundamental principles of equilibrium and compatibility. Strain limits for tension-controlled sections and compression-controlled sections are proposed that are consistent with the approach of the current and past ACI 318 Codes. The proposed method is compared with previously-reported experimental results, and the application of the proposed method is demonstrated by a numerical design example. Findings indicate that flexural members designed using the proposed design methods and criteria have comparable flexural strength characteristics with members designed according to current ACI 318 requirements, using Grade 60 (400 MPa) and Grade 75 (520 MPa) reinforcing steel.

Prospects for Percutaneous Valve Therapies

Developmental efforts to achieve percutaneous catheter-based therapies for cardiac valve repair and replacement have advanced rapidly over the past several years. A variety of methods to treat mitral regurgitation (MR) and to replace aortic and pulmonic valves have already been successfully employed in patients. These innovative clinical transcatheter valve therapies were anticipated more than a decade ago by creative experimentalists who helped develop predicate techniques in animal models. For example, in 1992, a catheter-delivered ball-in-cage prosthetic aortic valve was implanted in a canine model by Pavcnik1 and a stent-mounted bioprosthetic valve was placed by Andersen, who used a retrograde transarterial approach in a swine model.2 Clearly, the catheter-based technologies used in clinical studies today in patients with aortic stenosis were derived from the fusion of known successful aortic valve replacement (AVR) surgical devices and adaptive interventional modalities, first studied in experimental animal models. Similarly, approaches for transcatheter treatment of MR have also borrowed heavily from preexisting and accepted surgical techniques, such as the edge-to-edge leaflet coaptation technique and reduction ring mitral annuloplasty.3 Importantly, recognition that the coronary sinus parallels the mitral annulus has spurred unique catheter-based transvenous approaches to treat MR by indirectly reducing mitral annular dimensions.4 Because many of the new percutaneous approaches to valve therapy have been developed by surgeons, a collaboration has emerged between thoughtful surgeons and interventionalists, combining skill sets and experiences to accelerate the developmental pathways of less-invasive transcatheter valve therapies. Growing recognition exists that percutaneous alternatives to surgical therapies are required in some patient subgroups with valvular heart disease. Among patients with either mitral and/or aortic valve disease, an expanding population of elderly patients with significant comorbidities may benefit from traditional surgical methods, but these methods are associated with unacceptable perioperative mortality or prolonged postoperative recoveries. In the EuroHeart Survey …

Evaluation of electrospun PCL/gelatin nanofibrous scaffold for wound healing and layered dermal reconstitution

The current design requirement for a tissue engineering skin substitute is that of a biodegradable scaffold through which fibroblasts can migrate and populate. This artificial “dermal layer” needs to adhere to and integrate with the wound, which is not always successful for the current artificial dermal analogues available. The high cost of these artificial dermal analogues also makes their application prohibitive both to surgeons and patients. We propose a cost-effective composite consisting of a nanofibrous scaffold directly electrospun onto a polyurethane dressing (Tegaderm™, 3M Medical) – which we call the Tegaderm-nanofiber (TG-NF) construct – for dermal wound healing. Cell culture is performed on both sides of the nanofibrous scaffold and tested for fibroblast adhesion and proliferation. It is hoped that these studies will result in a fibroblast-populated three-dimensional dermal analogue that is feasible for layered applications to build up thickness of dermis prior to re-epithelialization. Results obtained in this study suggest that both the TG-NF construct and dual-sided fibroblast-populated nanofiber construct achieved significant cell adhesion, growth and proliferation. This is a successful first step for the nanofiber construct in establishing itself as a suitable three-dimensional scaffold for autogenous fibroblast populations, and providing great potential in the treatment of dermal wounds through layered application.

IP over optical cross-connect architectures [Topics in Optical Communications

IP over optical network architectures have been extensively discussed within the research literature over the past few years. However, although signaling protocols between IP routers and optical cross-connect networks have been standardized, large IP backbones are not typically deployed over optical cross-connect networks with automatic reconfigurability features, such as automatic restoration or dynamic establishment of new IP links. One of the most important criteria in determining whether an IP backbone should be carried over such an optical cross-connect network is economic viability. In this article we analyze and explore four architectures for a typical large ISP backbone. In contrast with some other published claims, our results suggest it is more economically attractive to bypass an intermediate cross-connect network, given current equipment and IP backbone network design requirements. However, for ISPs who also provide a large volume of private line services, we propose an integrated architecture for IP over optical cross-connect networks that may provide an attractive alternative for providing rapid and cost-effective restoration from network failures