Upstream Effects of Cazenovia Creek Ice-Control Structure

An ice-control structure (ICS) for Cazenovia Creek in West Seneca, N.Y., will arrest a breakup ice run and hold the resulting ice jam throughout typical breakup events. While this will reduce downstream flood damages, water levels upstream will be higher than under existing conditions, and upstream property owners must be compensated. We used HEC-RAS to model ice-jam hydraulics upstream of the ICS. Because the extent of the jam dictates the extent of high water, estimating ice-jam volume plays a key role in the modeling. The initial volume was the estimated prebreakup ice supply, less 30% transport losses. At each discharge, we reduced the available ice volume to account for melting by water entering the jam at 0.7°C and washouts through the ICS at a rate of 1% of discharge. These losses significantly reduce the ice-jam length, and thus the extent of high water, as discharge increases. The maximum ice-jam water levels at each discharge form an “elevation envelope” to determine the effect of the ICS on upstream property owners. To our knowledge, these are the first analyses to account for the effects of melting and washout losses on predicted ice-jam water levels.     

Assessing the Performance of a Sloped-Block Ice-Control Structure

Hardwick, Vt., having experienced 10 ice-jam floods in 30?years, has not experienced one since construction of a sloped-block ice-control structure (ICS) in 1994. This innovative structure consists of four sloped granite blocks spaced across the Lamoille River upstream of the village and adjacent to a treed floodplain. It arrests ice runs, forms partially grounded jams, and retains these jams for hours to days. The measured ice-hydraulic characteristics of the breakup runs and resulting ice jams (e.g., wave celerities and amplitudes, porous-flow seepage coefficients) are similar to characteristics obtained from the 1:10-scale model tests used to develop the structure. Seepage coefficients, and hence jam porosities, generally increase with increasing discharge, and only two breakup events have caused floodplain flow. Water temperatures of 0.1–0.3°C measured during a breakup event confirm that ice melting can account for the rate of porosity increase. Field and model data indicate that ice-jam holding time and jam-release discharge increase with increasing ice-piece thickness to a threshold of 6–7% of ICS gap width, beyond which no releases occur. Consistency between prototype and model ice-hydraulic characteristics and ice-holding capacity reinforce the conclusion that the sloped-block ICS can reliably retain ice jams during breakup events that pose the greatest flood threat: thick, strong ice, and large breakup waves. This ice-retention behavior can account for the observed reduction in ice-jam flooding in Hardwick during the past 11 seasons.     

Low-Cost Ice-Control Structure

Communities located on small, northern rivers can experience severe breakup ice jams. While flood damages may be significant locally, they are often insufficient to justify the cost of conventional flood-control structures. Environmental concerns also tend to render these structures unattractive. A new, low-cost structure appears to be well suited to control breakup ice jams on small rivers. It consists of massive sloped blocks, partially buried in riprap, placed across the river adjacent to a natural floodplain. The blocks will arrest a breakup ice run and form a stable, partially grounded ice jam. Trees or boulders on the floodplain retain ice pieces in the river channel while allowing flow to bypass the structure. Large gaps between blocks allow easy fish and canoe passage. Refrigerated hydraulic model tests indicate that the structure should perform well even during severe breakup events. A prototype built in Hardwick, Vt., has performed well during the four mild breakup events experienced to date. Its cost of $3,600∕m of river width represents about an order-of-magnitude reduction compared with previous ice-control structures.     

Formation of Breakup Ice Jams at Bridges

Bridges can impede the passage of river ice during the breakup event and promote formation of ice jams, with adverse socioeconomic and ecological impacts. Design for ice passage at bridges has largely been empirical and qualitative so that avoidance of ice-jam instigation is often uncertain. It is thus important to develop rational design criteria, based on a thorough understanding of the factors governing the interaction between bridges and ice. This concern is quantified by utilizing recent advances on breakup initiation and comparing driving and resisting forces when the sheet ice cover is about to be set in motion. Retention of ice sheets by in-stream piers can lead to jamming via accumulation of ice rubble that may be arriving from upriver. The resulting methodology is applied to two case studies and yields results that are in full accord with local experience. Though the present findings pertain to the obstruction created by in-stream piers, similar reasoning can be applied to constrictions that may be caused by protruding bridge abutments.     

Design and Experimental Study of a Harp-Shaped Single Span Cable-Stayed Bridge

This paper presents issues in the design concept, analysis, and test results of a harp-shaped single span cable-stayed bridge, Hongshan Bridge, located in Changsha, Hunan Province, China. The bridge has a 206 m span, with a pylon inclined at 58° from the horizontal and 13 pairs of parallel cable stays without a back?stay. This paper discusses the design approach for the main components of the bridge. Emphasis will be put on the following three aspects. First, the weight of the pylon and all dead loads of the main girder in addition to part of the live loads must be in a balanced condition. Second, the main girder should be an orthotropic steel-concrete composite box girder because of the superior safety and weight reduction of this type of structure. Third, the cable?stays should be anchored at the neutral axis of the pylon to prevent the development of high secondary moments caused by other anchor approaches. Furthermore, based on results from tests carried out on three models, namely, scaled full model tests in a scale of 1:30, scaled section model tests in a scale of 1:6, and wind tunnel tests, the following four key issues were studied: (1) the local stability of orthotropic steel-concrete composite box girder subjected to combined bending and axial loads; (2) the characteristics under loads of 13-m-long cantilever beams; (3) the safety of the bridge under some other dangerous conditions; and (4) the characteristics of wind resistance and wind tunnel testing.     

Performance of a Tied-Arch Reinforced Concrete Railway Bridge: Rating, Safety Assessment, and Bond Length Evaluation

This study presents investigations regarding visual inspection, dynamic testing, and finite-element modeling of an approximately 80-year old reinforced concrete tied-arch railway bridge that is still in service in Turkey. Investigations were conducted as part of a systematic periodic inspection along Ankara-Zonguldak railway line. The bridge is subject to heavy freight trains with increasing axle loads. Field tests such as material tests and dynamic tests were used to calibrate the finite-element model of the bridge. Detailed information regarding testing and model updating procedure is given. Based on test results, computer model was refined. The calibrated model of the bridge structure was then used for structural assessment and evaluation. Despite sufficient overall safety, local details were found to be problematic. Due to insufficient bond length in hanger-to-arch connection, a strengthening scheme using steel channel sections was proposed.     

Evaluation of In-Service Performance of Tom’s Creek Bridge Fiber-Reinforced Polymer Superstructure

The Tom’s Creek Bridge is a small-scale demonstration project involving the use of fiber-reinforced polymer (FRP) composite girders as the main load-carrying members. The project is intended to serve two purposes. First, by calculating bridge design parameters such as the dynamic load allowance, transverse wheel load distribution, and deflections under service loading, the Tom’s Creek Bridge aids in modifying current American Association of State Highway and Transportation Officials bridge design standards for use with FRP composite materials. Second, by evaluating the FRP girders after exposure to service conditions, the project begins to answer questions about the long-term performance of these advanced composite material beams when used in bridge design. This paper details the in-service analysis of the Tom’s Creek Bridge. Five load tests, at 6-month intervals, were conducted on the bridge. Using midspan strain and deflection data gathered from the FRP composite girders during these tests, the aforementioned bridge design parameters have been determined. The Tom’s Creek Bridge was determined to have a maximum dynamic load allowance, IM, of 0.90, a transverse wheel load distribution factor, g, of 0.101, and a maximum deflection of L/490. Two bridge girders were removed from the Tom’s Creek Bridge after 15 months of service loading. These FRP composite girders were tested at the Structures and Materials Research Laboratory at Virginia Tech for stiffness and ultimate strength and compared to preservice values for the same beams. These measurements indicate that, after 15 months of service, the FRP composite girders have not significantly changed in stiffness or ultimate moment capacity.     

Discharge Coefficient for Sharp-Crested Side Weir in Subcritical Flow

To estimate the outflow over a rectangular sharp-crested side weir, the discharge coefficient in the weir equation needs to be known. Although this type of structure has been designed and used extensively by hydraulic engineers, a universally acceptable discharge coefficient does not exist. In this study over 250 laboratory tests were conducted, and the results were analyzed to find the influence of the flow hydraulics and the geometric, channel, and weir shapes on the coefficient. The results show that for subcritical flow the De-Marchi assumption of constant energy is acceptable, and the weir discharge can therefore be used. Furthermore, it was discovered that the De-Marchi coefficient of discharge is a function of the upstream Froude number and the ratios of weir height to upstream depth and weir length to channel width, whereas the channel slope in subcritical flow can be ignored. Hence, an accurate equation for the coefficient of discharge is introduced.     

Ice Boom Simulations and Experiments

A three-dimensional discrete element model (DEM) was developed to simulate ice boom operation in a rectangular channel. The model simulates the motion of each individual ice floe, the interaction between adjacent floes, the interaction of the floes with the walls and boom, and the water drag applied to the floes on the underside of the ice accumulation. The DEM simulations were compared with a parallel set of physical model tests using natural ice. The DEM successfully reproduced the observed magnitude and distribution of the forces on the boom and the channel sides as the boom retained a surge of drifting ice. Variations in channel side roughness produced similar changes in the division of forces between the boom and sidewalls in the simulations and model tests. Finally, the load distribution between the boom and the channel sides and the effect of channel side roughness in the context of granular ice-jam theory were analyzed.     

考虑桩土相互作用的大跨度钢拱桥地震反应分析

为了研究桩土相互作用下大跨度钢拱桥的地震反应特点以及塑性铰的形成部位和发展过程,利用ANSYS有限元程序对比研究了在多组地震输入条件下,考虑基础固结和桩土相互作用下的动力特性及在罕遇地震下的地震反应,并探讨了层状场地土对桩基以及上部结构的影响.结果表明:与基础固结模型相比,考虑桩土相互作用体现了土的特性对结构的影响,较好地反映了结构的动力特性,结构的自振周期延长,且对高阶振型周期影响显著;同时结构各部位的内力响应呈下降趋势,位移响应被放大,但受边界假定的影响,其总体反应趋势未发生改变,其中在主梁1/4处、梁拱结合处以及柱底处均出现塑性铰,且柱底处率先屈服,各塑性铰区的变形仍控制在较小的范围内,桩身则未出现塑性铰.     

中间包结构优化的水模型正交试验

通过1:3水力学模型,按L16(4~5)正交表进行正交试验,研究和优化34 t中间包的结构。结果表明,中间包结构主要主次关系为坝高、堰与长水口间距、坝堰间距,堰深;最佳结构组合为坝高135mm,堰深90mm、坝堰间距155mm,堰与长水口间距为195mm。与原工况比较,优化方案的综合评分值从74.32提高到91.01。     

Evaluation of the Effectiveness of Strengthening Intervention by CFRP on MRWA Bridge No. 3014

Main Roads of Western Australia has a continuing program of bridge upgrading, to refurbish and strengthen bridges to allow for increasing vehicle traffic and increasing axle loads. A 40-year-old, four-span reinforced concrete slab bridge was retrofitted with application of CFRP laminate strips on the top of the deck over the piers, as well as on the deck soffit in the midspan regions, to reduce high moments in both hogging and sagging. The dynamic assessment of the bridge before and after strengthening works provided the opportunity to evaluate the effectiveness of the strengthening intervention through dynamic measurements. A performance evaluation of the repaired structure was carried out through traffic loading application on the updated numerical models of the bridge, before and after retrofit. As a main observation, the addition of CFRP laminate strips led to a significant increase of the structural capacity in flexure. The paper discusses the results obtained from the dynamic-based assessment in terms of effectiveness of the strengthening intervention as well as of efficiency in using such a methodology to evaluate the capacity increase of the retrofitted bridge.     

Laboratory and Field Testing of Composite Bridge Superstructure

Bridge rehabilitation utilizing a hybrid fiber-reinforced polymeric composite has recently been completed in Blacksburg, Va. This project involved replacing the superstructure in the Tom's Creek Bridge, a rural short-span traffic bridge with a timber deck and corroded steel girders, with a glue-laminated timber deck on composite girders. To verify the bridge design and to address construction issues prior to the rehabilitation, a full-scale mock-up of the bridge was built and tested in the laboratory. This setup utilized the actual composite beams, glue-laminated timber deck panels, and the skewed geometry implemented in the rehabilitation. Following rehabilitation, the bridge was field tested under controlled conditions (vehicle load and position). Both tests examined service load deflections, girder strains, load distribution, degree of composite action, interpanel deck deflections, and impact factor. The field test results indicate a service load deflection of L∕400 under moving loads and a high factor of safety in the composite members against material failure. The data from the field test serve as a baseline reference for future field durability assessments as part of a long-term performance and durability study.     

具有加热功能的四流连铸中间包合理结构及挡墙设置的研究

为配合等离子中间包加热工程，冶金部鞍山热能研究院根据连铸中间包等离子加热工程的需要，在原有四流中间包的基础上重新设计了具有加热功能的中间包，并进行了水力模型试验，确定了合理的中间包结构和挡墙设置，对进一步提高铸坯质量直到一定作用。     

Vehicle Collision with Bridge Piers

Inelastic transient finite element simulations are used to investigate the demands generated during collisions between vehicles and bridge piers. Such collisions have occurred in the past, sometimes with catastrophic consequences. Two different types of trucks and two different bridge/pier systems are used in the simulations. The approach speeds for the trucks range from 55 to 135 kph. Various quantities of interest are extracted from the finite element results and used to develop a better understanding of the vehicle/pier crash process and to critique current specifications addressing such events. Although physical vehicle–pier impact tests were not carried out as part of this research, a variety of exercises are conducted to provide confidence in the analysis results. The simulations show that current collision design provisions could be unconservative and that there may be a population of bridge piers that are vulnerable to accidental or malicious impact by heavy trucks.     

Shear Retrofit of Hollow Bridge Piers with Carbon Fiber-Reinforced Polymer Sheets

Hollow bridge piers are currently being used in high-speed rail and highway projects in Taiwan. The flexural ductility and shear capacity of such piers with the configuration of lateral reinforcement used in Taiwan has recently been studied.?This paper reports that circular and rectangular hollow bridge piers retrofitted by carbon fiber-reinforced polymer (CFRP) sheets were tested under a constant axial load and a cyclic reversed horizontal load to investigate their seismic behavior, including flexural ductility, dissipated energy, and shear capacity. An analytical model is also developed to predict the moment-curvature relationship of sections and the lateral load-displacement relationship of piers. Based on the test results, the seismic behavior of such piers is presented. The test results are also compared with the proposed analytical model. It was found that the ductility factors of the tested piers ranged from 3.3 to 5.5 and that the proposed analytical model could predict the lateral load-displacement relationship of such piers with reasonable accuracy. All in all, CFRP sheets can effectively improve both the ductility factor and the shear capacity of hollow bridge piers.     

Development of FRP Short-Span Deployable Bridge—Experimental Results

For military and civilian applications, there exists a need for lightweight, inexpensive, short-span bridges that can be easily transported and erected with minimal equipment. Owing to its favorable properties, fiber-reinforced polymer (FRP) has been shown to be feasible for the construction of such bridges. Investigations into the behavior of a short-span bridge structural concept, adapted to the material properties of commercially available glass FRP (GFRP) pultruded products, are presented. A 4.8-m span prototype was built from GFRP sections, bonded throughout to form a tapered box beam, with a width of 1.2?m and a height at midspan of approximately 0.5?m. The box beam represents a single trackway of a double-trackway bridge, whose trackways could be connected by light structural elements. The quasi-static and dynamic behavior of the prototype box beam was investigated in ambient laboratory and field conditions to assess the design and construction techniques used, with a view to designing a full-scale 10-m GFRP bridge. Laboratory testing of the prototype box beam used single and pairs of patch loads to simulate wheel loading. These tests confirmed that the box beam had sufficient stiffness and strength to function effectively as a single trackway of a small span bridge. Field testing of the structure was undertaken using a Bison vehicle (13,000?kg), driven at varying speeds over the structure to establish its response to realistic vehicle loads and the effects of their movement across the span.     

浅谈钢实腹梁人行桥结构设计

西北铅锌厂为解决人车分流交通问题,需在原入口桥两侧修建人行交通桥,交通桥标准跨度30m,桥面净宽度3.6 m,桥身结构为钢结构,整座钢桥跨度大,结构稳定性计算较为复杂,本文简要介绍了人行桥上部结构的设计情况和计算方法。     

Design of FRP Jackets for Upgrade of Circular Bridge Piers

The upgrading of bridges located in seismic areas and built according to obsolete codes is becoming a priority task for highway administrations. Among the possible upgrading strategies, the use of fiber-reinforced plastic (FRP) jackets is gaining widespread acceptance. In this paper, a design equation is proposed to determine the optimal thickness of FRP jackets, to enhance the ductility of existing reinforced-concrete (RC) bridge piers with circular cross sections. The design procedure stems from the definition of an upgrading index, given as the ratio of the target to availability ductility at the pier base section, to be attained through FRP jacketing. The available ductility is that identified through the usual assessment procedures on the RC member set for upgrade, whereas the target ductility is evaluated based on the expected actions on the bridge. The upgrading index is initially defined in general terms and is subsequently extended to the case of piers built in seismic regions. It results in a simple expression in terms of easily computable quantities, such as the ultimate strain and the peak strength of concrete, before and after upgrading. A parametric study on old-code–designed bridge pier sections, upgraded with either glass or carbon fiber jackets, is performed based on a fiber-section model equipped with a newly developed FRP-confined concrete model. This study shows that the index, despite its simplicity, yields excellent predictions of the ductility increase obtained through FRP wrapping, and it is therefore used to develop a design equation. The equation allows the design of the optimal thickness of FRP jackets in terms of the desired upgrading index, mechanical characteristics of the selected composite material, and quantities defining the initial state of the pier section. The design procedure has been applied to available experimental tests of a scaled bridge pier wrapped with FRP and tested to failure, and it has been demonstrated to be very effective.     

Application of Riprap and Collar to Prevent Scouring around Rectangular Bridge Piers

Various methods to control scour around bridge piers have been proposed, including application of riprap and installing a collar around piers. In the present study application of riprap alone and a combination of riprap and collar were examined experimentally for scour control around rectangular bridge piers. Piers aligned with the flow and skewed at 5, 10, and 20° to the flow were tested. Piers with three different aspect ratios equal to 1:3, 1:5, and 1:7 were used in this study. A collar three times wider than the piers’ width was installed around the piers at the streambed level. All experiments were conducted at the threshold of motion of the bed material. The size and extent of stable riprap stones for prevention of scouring around the piers was found by experiment with and without the collar. A method previously given for calculating stable riprap size around circular piers is extended for rectangular piers with different aspect ratios and skew angles with and without collar protection. The extent of stable riprap layer in all tests is also presented.