Review of Live Load Impact Factor for Existing Truss Railroad Bridges in the United States

2013 ◽  
Author(s):  
David W. Jacobs ◽  
Ramesh B. Malla
Keyword(s):  
Impact Factor ◽  
Energy Efficient ◽  
High Speed ◽  
The United States ◽  
Live Load ◽  
Railroad Bridges ◽  
Long Span ◽  
Railway Engineering ◽  
Significant Effort ◽  
Load Impact

The current American Railway Engineering and Maintenance-of-Way Association (AREMA) Manual provides live load impact formulas for the design of steel railroad bridges. The only variable in those formulas is span length and do not include other parameters that bridge engineers know affects live load impact factor. Years of use in practice and research have shown that these formulas are reliable, safe and simple to apply, though often very conservative. In order to make the nation’s transportation more efficient and energy efficient, a significant effort is underway in the U.S. to enhance its railroad infrastructures. Bridges built before the 1950s, many of which are still in service, were designed to sustain the effects of steam engine hammer blow, and consequently slow speed. Yet, most of these bridges may not be replaced and may be required to carry high speed passenger equipment. This raises the question of what effects higher speed trains will have on old, long span truss steel bridges. This paper presents finding from the detail literature review on the current live load impact factor on truss railroad bridges and its implication to the future.

Securing Niagara (1852–55)

2020 ◽  
pp. 344-395
Author(s):  
Richard Haw
Keyword(s):  
United States ◽  
Suspension Bridge ◽  
The United States ◽  
Railroad Bridges ◽  
Long Span ◽  
Runaway Slaves ◽  
The Impact ◽  
Egyptian Architecture

The Niagara contract was a fitting judgment on John’s career to date, and the bridge itself was a triumph, eliciting praise and admiration from all over the globe, for both its handsome Egyptian architecture and the soundness of its design. It took four years to build and was the world’s first railroad suspension bridge, or at least the first successful one, fully demonstrating the strength and effectiveness of the suspension plan for heavy-going freight. It also compared very favorably with Robert Stephenson’s recently completed Britannia Tubular Bridge, the British engineer’s rival solution to the problem of long-span railroad bridges. A lifelong, committed abolitionist who wrote extensively about the evils of slavery, John also appreciated the impact his bridge had (somewhat incidentally) on the institution of slavery. Harriet Tubman (among others) used John’s bridge numerous times in the late 1850s to lead runaway slaves out of the United States and into British Canada.

Effects of the highway live load on the additional forces of the continuously welded rails of a long-span suspension bridge

2021 ◽  
pp. 095440972110619
Author(s):  
Xiangdong Yu ◽  
Nengyu Cheng ◽  
Haiquan Jing
Keyword(s):  
High Speed ◽  
Suspension Bridge ◽  
Additional Stress ◽  
Live Load ◽  
Analysis Model ◽  
Maximum Displacement ◽  
Obvious Effect ◽  
Long Span Bridges ◽  
Long Span ◽  
Track Bridge

High-speed running trains have higher regularity requirements for rail tracks. The track-bridge interaction of long-span bridges for high-speed railways has become a key factor for engineers and researchers in the last decade. However, studies on the track-bridge interaction of long-span bridges are rare because the bridges constructed for high-speed railways are mainly short- or moderate-span bridges, and the effects of the highway live load on the additional forces of continuously welded rails (CWRs) have not been reported. In the present study, the effects of the highway live load on the additional forces of a CWR of a long-span suspension bridge are investigated through numerical simulations. A track-bridge spatial analysis model was established using the principle of the double-layer spring model and the bilinear resistance model. The additional stress and displacement of the rail are calculated, and the effects of the highway live load are analyzed and compared with those without a highway live load. The results show that the highway live load has an obvious effect on the additional forces of a CWR. Under a temperature force, the highway live load increases the maximum tensile stress and compressive stress by 10 and 13%, respectively. Under a bending force, the highway live load increases the maximum compressive rail stress and maximum displacement by 50 and 54%, respectively. Under a rail breaking force, when the highway live load is taken into consideration, the rail displacement at both sides of the broken rail varies by 50 and 42%, respectively. The highway live load must be taken into consideration when calculating the additional forces of rails on highway-railway long-span bridges.

Dynamic Interaction Aspects of Cable-Stayed Guideways for High Speed Ground Transportation

1974 ◽  
Vol 96 (2) ◽  
pp. 180-192 ◽  
Author(s):  
S. G. Meisenholder ◽  
P. Weidlinger
Keyword(s):  
Elastic Foundation ◽  
Conceptual Design ◽  
Traveling Wave ◽  
High Speed ◽  
Dynamic Interaction ◽  
Design Approach ◽  
Live Load ◽  
Beam On Elastic Foundation ◽  
Long Span ◽  
Cable Stays

This paper describes the dynamic considerations in the design of a long span (200 to 600 ft) cable-stayed guideways for future tracked levitated vehicles (TLV’s) which will be used for high speed ground transportation. A design approach is described in which a cable-stayed guideway structure can be synthesized to simulate the behavior of a beam on elastic foundation. This result is achieved by the “cable-tuning” approach, in which the cable stays are selected to achieve an equivalent uniform elastic foundation. The design approach insures that the live load deflection of the trackway beam is manifested as a traveling wave which moves horizontally at the same velocity as the vehicle, thereby minimizing dynamic interaction problems. Parametric results are presented for the dynamic response of a beam on elastic foundation. Optimum cable and tower configurations are developed for this guideway concept and a typical conceptual design is described.

On live load impact factors for railroad bridges

2019 ◽  
Vol 7 (4) ◽  
pp. 262-278 ◽  
Author(s):  
David W. Jacobs ◽  
Ramesh B. Malla
Keyword(s):  
Impact Factors ◽  
Live Load ◽  
Railroad Bridges ◽  
Load Impact

High-Speed Rail—Coming to America?

2009 ◽  
Vol 19 (2) ◽  
pp. 261-265
Author(s):  
David Ossian Cameron
Keyword(s):  
United States ◽  
Economic Development ◽  
Energy Efficient ◽  
High Speed ◽  
The United States ◽  
High Speed Rail ◽  
Positive Economic ◽  
The World ◽  
Economic Stimulus ◽  
Stimulus Package

The United States lags many parts of the world when it comes to high-speed rail. But investing in high-speed rail could help us through current problems. Funds—$8 billion—in the economic stimulus package passed by Congress are designated for high-speed rail. Other funds in the pipeline total approximately $15.5 billion. High-speed rail can relieve congestion, free up national airspace, provide reliable transportation and positive economic development, create jobs, and is more energy efficient than other modes of travel.

Standard Midwest Guardrail System Placed at 1V:2H Slope Break Point or with Omitted Post

2017 ◽  
Vol 2638 (1) ◽  
pp. 65-76
Author(s):  
Karla A. Lechtenberg ◽  
Robert W. Bielenberg ◽  
Scott K. Rosenbaugh ◽  
Ronald K. Faller ◽  
John D. Reid
Keyword(s):  
High Speed ◽  
Break Point ◽  
The United States ◽  
Safety Performance ◽  
Performance Criteria ◽  
Safety Hazards ◽  
Long Span ◽  
Level 3 ◽  
Occurrence State ◽  
And Behavior

State departments of transportation (DOTs) throughout the United States commonly use W-beam guardrail systems to keep errant vehicles from leaving high-speed roadways and encountering safety hazards adjacent to the roadway edge, such as steep roadside slopes. Additionally, although W-beam guardrail is used to protect errant vehicles from safety hazards along the roadways, obstructions at post locations within a run of guardrail are a common occurrence. State DOTs wanted to evaluate the standard Midwest Guardrail System (MGS) for use in these instances. First, the standard MGS with 6-ft (1,829-mm) W6 × 8.5 (W152 × 12.6) steel posts spaced at 75 in. (1,905 mm) placed at the slope break point of a 1V:2H slope was successfully crash tested and evaluated according to the Test Level 3 (TL-3) safety performance criteria presented in the Manual for Assessing Safety Hardware (MASH). Subsequently, the standard MGS with one omitted post, which created an unsupported span of 12.5 ft (3.8 m), was full-scale crash tested, and it satisfied the MASH TL-3 safety performance criteria. Because multiple variations of the MGS system have been developed for special applications, recommendations for the omission of a post or installation on a steep slope will vary depending on the nature and behavior of the application. The safety performance of various MGS configurations and special applications was compared. Implementation guidance was then given about the use of the MGS placed at the slope break point and omitting a post in the MGS with MGS special applications. These special applications included terminals and anchorages, MGS stiffness transition to thrie beam approach guardrail transitions, MGS long-span system, MGS adjacent to 1V:2H fill slopes, MGS on 1V:8H approach slopes, MGS in combination with curbs, wood post MGS, and MGS without blockouts.

Live-Load Girder Distribution Factors for Bridges Subjected to Wide Trucks

2000 ◽  
Vol 1696 (1) ◽  
pp. 144-149 ◽  
Author(s):  
Sami W. Tabsh ◽  
Muna Tabatabai
Keyword(s):  
Finite Element ◽  
The United States ◽  
Live Load ◽  
Wheel Load ◽  
Element Analysis ◽  
Load Effect ◽  
Design Specifications ◽  
Girder Bridges ◽  
Girder Distribution Factors ◽  
Modification Factor

An important problem facing engineers and officials in the United States is the constraint imposed on transportation due to limitations of bridges. These limitations typically constrain vehicles to minimum heights and widths, to minimum and maximum lengths, and to a maximum allowable weight. However, with current demands of society and industry, there are times when a truck must carry a load that exceeds the size and weight of the legal limit. In this situation, the trucking company requests from the state departments of transportation an overload permit. For a truck with a wheel gauge larger than 1.8 m (6 ft), the process of issuing a permit for an overload truck requires a tremendous amount of engineering efforts. This is because the wheel load girder distribution factors (GDFs) in the design specifications cannot be used to estimate the live-load effect in the girders. In some cases, an expensive and time-consuming finite element analysis may be needed to check the safety of the structure. In this study, the finite element method is used to develop a modification factor for the GDF in AASHTO’s LRFD Bridge Design Specifications to account for oversized trucks with a wheel gauge larger than 1.8 m. To develop this factor, nine bridges were considered with various numbers of girders, span lengths, girder spacings, and deck slab thicknesses. The results indicated that use of the proposed modification factor with the GDF in the design specifications can help increase the allowable load on slab-on-girder bridges.

scholarly journals Dual-shot dynamics and ultimate frequency of all-optical magnetic recording on GdFeCo

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Sicong Wang ◽  
Chen Wei ◽  
Yuanhua Feng ◽  
Hongkun Cao ◽  
Wenzhe Li ◽  
...  
Keyword(s):  
Magnetization Reversal ◽  
Energy Efficient ◽  
High Speed ◽  
Data Transfer ◽  
Laser Pulses ◽  
Time Resolved ◽  
All Optical ◽  
Fs Laser ◽  
High Speed Data ◽  
Natural Way

AbstractAlthough photonics presents the fastest and most energy-efficient method of data transfer, magnetism still offers the cheapest and most natural way to store data. The ultrafast and energy-efficient optical control of magnetism is presently a missing technological link that prevents us from reaching the next evolution in information processing. The discovery of all-optical magnetization reversal in GdFeCo with the help of 100 fs laser pulses has further aroused intense interest in this compelling problem. Although the applicability of this approach to high-speed data processing depends vitally on the maximum repetition rate of the switching, the latter remains virtually unknown. Here we experimentally unveil the ultimate frequency of repetitive all-optical magnetization reversal through time-resolved studies of the dual-shot magnetization dynamics in Gd27Fe63.87Co9.13. Varying the intensities of the shots and the shot-to-shot separation, we reveal the conditions for ultrafast writing and the fastest possible restoration of magnetic bits. It is shown that although magnetic writing launched by the first shot is completed after 100 ps, a reliable rewriting of the bit by the second shot requires separating the shots by at least 300 ps. Using two shots partially overlapping in space and minimally separated by 300 ps, we demonstrate an approach for GHz magnetic writing that can be scaled down to sizes below the diffraction limit.

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