Engineering analysis and design software
Civil and Structural engineering

Case Study

Analysis of Barge Gate and Gate Abutment Structures

  • Optimization of steel plate flood defence gates in New Orleans

  • Noticeably faster modelling and analysis with LUSAS than previously obtained

  • Tight design schedule met

INCA Engineers Inc. based in Bellevue, WA, is using LUSAS Civil and Structural to assist with the design of flood protection structures on two contracts awarded to it by the United States Army Corps of Engineers (USACE), New Orleans District. By using LUSAS to help with the design of a floating barge gate and associated abutment structures the gate design could be optimized to meet design criteria and a tight design schedule could be met.

Overview

On 29th August 2005, Hurricane Katrina, an extremely large and powerful storm, overwhelmed the flood and storm defences at several locations in and around New Orleans causing large-scale loss of life and extensive damage to property. To help prevent future flooding the hurricane protection system of levees, pump stations and flood gates that encircle the most at-risk parts of the city is being strengthened to create a stronger, flood and storm reduction system that will give a once-in-100-years level of protection.

Satellite image of Hurricane Katrina approching New Orleans

INCA involvement

Interim flood protection and the provision of storm gates at Bayou Segnette Pump Station and the introduction of an interim floodwall and storm gates along Company Canal in Jefferson Parish are just two of many USACE contracts that are currently undergoing design or construction. For Bayou Segnette Pump Station INCA designed a 30-foot-wide vertical lift gate that would be powered electrically but also have a manual back up lowering system. For the Company Canal INCA designed a barge gate that could be floated from a stored location into its closed storm position prior to a potential flooding event. Between storm gates INCA also designed a series of "A-Frames" that provided lateral restraint for the sheet pile cut off. The estimated construction cost for these two projects alone lies in the region of $20,000,000.

Barge Gates and Abutments

The barge gate abutments for the Company Canal are founded on raked HP14x117 section steel piles which support a 34-0" x 16-0" x 45" thick concrete pile cap. Steel bracing struts are built into and bolted onto the pile cap to support the steel wall framing members which are comprised of steel plate varying between 1/2" and 1" thickness. The barge gate has a 45 feet clear opening with a sill elevation at -8.00 and still water level at elevation 9.00. The barge is approximately 15 feet wide and 47 feet long. When in the closed position the gate is ballasted down and in-service reactions are taken by the two steel abutment frames.

Modelling with LUSAS

All of the structural features of the abutments were combined into one LUSAS model using beam, shell and solid elements to appropriately model each structural element. Use of the groups facility permitted easy isolation of each structural type for display and model building purposes and also enabled customized displays of assigned attibutes to be created as used, for example, when checking the correct assignment of steel plate thicknesses - a key requirement for these diaphragm-type of structures. High and still water level, gate, barge and impact loadings were all considered in the linear static analysis that was carried out. A separate LUSAS model was used to analyse the forces on the floating barge due to hydraulic loads.

Gate abutment piles and pilecap

LUSAS model of barge gate abutment Colour coded plot showing abutment steel plate thicknesses

Modelling of piled supports 

LUSAS model of barge gate abutment with pile cap (blue) and steel bracing and walling (green) Colour coded plot showing abutment steel plate thicknesses
     

Typical load combinaton stresses in a gate abutment structure

David Stensby, Structural Engineer at INCA said: "The barge gate design had to be done under very tight schedule constraints. The fact that the diverse elements of the abutment structure could all be modelled efficiently in the same LUSAS model was especially useful, as indeed was the ability to accurately model the water pressure loading on the barge model."

Results

Results for each of the loadcases were investigated and load combinations were created to derive combined effects of different permutations of the self-weight, gate, flood and impact loading. In areas of interest the LUSAS section slice facility allowed localised stresses to be checked. David Stensby confirmed the usefulness of the results: "The stresses and deflections that we obtained from the LUSAS modelling allowed us to adjust the gate design as necessary to meet the design criteria."

James Costello, Project Manager at INCA summed it up as follows: "LUSAS really shined on the modelling and analysis of these steel barge closure structures and as a result it helped us to meet the tight design schedule. The time taken to model these structures in LUSAS was noticeably reduced over that taken when we previously modelled similar structures with other analysis packages."

LUSAS model of barge gate Barge gate steel plate thicknesses used
LUSAS model of barge gate Barge gate steel plate thicknesses used 
(upstream and deck plates not shown for clarity)
 
Typical load combination stresses in a barge structure

"LUSAS really shined on the modelling and analysis of these steel barge closure structures and as a result it helped us to meet the tight design schedule. The time taken to model these structures in LUSAS was noticeably reduced over that taken when we previously modelled similar structures with other analysis packages."

James Costello, Project Manager, INCA Engineers Inc.


 

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