Supplemental_Documents.pdf

Structural Plate Design Guide

MULTI-PLATE®

Aluminum Structural Plate

Aluminum Box Culvert

SUPER-SPAN™

BridgeCor®

Steel EXPRESS® Foundations

8th Edition

ENGINEERED SOLUTIONS

Steel and Aluminum Structural Plate Design Guide

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Steel and Aluminum Structural Plate Design Guide Table of Contents

This design guide is provided by Contech Engineered Solutions to assist designers with most applications and design aspects of MULTI-PLATE®, Aluminum Structural Plate (ALSP), Aluminum Box Culverts (ALBC), SUPER-SPAN™, SUPER-PLATE®, BridgeCor®, and Steel EXPRESS®. To support the designer, this written guide along with the provided standard details can be used to assist in the preparation of the project plans and specifications. For additional information, contact your local Contech representative or call 800-338-1122 to find a Contech representative near you.

Typical Design Steps Selection of Structure Shape Designing for Service Life Structural Plate Design

MULTI-PLATE and ALSP

ALBC

SUPER-SPAN and SUPER-PLATE BridgeCor

Minimum Cover over Plate Structures Structure End Treatments Material Design and Installation Specs

MULTI-PLATE®

Product Overview Bolts and Nuts Round Vertical Ellipse Pipe Arch Single Radius Arch Horizontal Ellipse Underpass Project Specifications

Aluminum Structural Plate Product Overview Bolts and Nuts Handling Weights & Plate Make-Up Height of Cover Table Instructions Round Ellipse Pipe Arch Single Radius Arch Underpass Project Specifications

Aluminum Box Culvert Product Overview

HL-93

H-20/HS-20

H-25/HS-25

Aluminum Box Culverts Plate Make-Up Prefabricated Aluminum Headwalls Prefabricated Aluminum Full Invert Prefabricated Aluminum Footing Pads Project Specifications

SUPER-SPAN™/SUPER-PLATE®

Product Overview Steel Project Specifications Aluminum Project Specifications

BridgeCor®

Product Overview Project Specifications BridgeCor External Rib System Round Design Details Single Radius Arch Design Details 2-Radius Arch Design Details Box Culvert Design Details

Steel EXPRESS® Foundations Product Overview Project Specifications

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Outline of Typical Design Steps The following steps describe a basic, typical procedure for designing a structural plate bridge or culvert but are not intended to represent all possible considerations that a prudent designer should investigate. Although not all of these steps will be covered in this document, additional design aids are available. If the designer has questions regarding an aspect of structure designs, the designer can contact the local Contech representative for additional information.

This guide follows the design methodology of the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications. The height of cover tables will vary when a different design method is followed. An HL-93 live load structural check determines if an HS-20 or a tandem axle vehicle controls. For other design load considerations, please contact your local Contech representative.

Design Sequence

1. General Structure Selection

• Guidelines for selection of hydraulic, roadway, pedestrian, or grade separation structure

requirements, if applicable

3. Check Service Life and Protection of Structure from Environment

x American Association of State Highway and Transportation Officials (AASHTO) LRFD or 2002 Standards

(NCSPA)

x American Railway Engineering and Maintenance

Association (AREMA)

x For arch structures, a reinforced concrete footing may be required. Please see page 108 for Contech's Steel EXPRESS® Foundation option.

• Backfill envelope – backfill recommendations

References

1. AASHTO Material, Design, and Installation Specifications

• MULTI-PLATE, SUPER-SPAN, Aluminum Structural Plate, Box Culvert and BridgeCor – material design and installation

• Project specifications

designer upon request.

3. An NCSPA Corrugated Steel Pipe Design Manual is available from the NCSPA or your local Contech representative. More specific information on each step or topic is available from Contech Engineered Solutions.

These are the basic steps involved in designing a corrugated flexible structure. This guide contains specific information about MULTI-PLATE, Aluminum Structural Plate, Aluminum Box Culverts, SUPER-SPAN/SUPER-PLATE, and BridgeCor.

* � Hydraulic nomographs and FHWA HY-8 program assistance is available from your local Contech representative.

** Structures can be load rated according to AASHTO LRFR methodology, please contact your Contech representative for the NCSPA Design Data Sheet 19, which may be used for guidance.

Design Guide

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STRUCTURE SHAPE GEOMETRY

Shapes Span x Rise Common Uses Steel Aluminum Trade Name

Round 5’ to 50’-6” Culverts, storm sewers, aggregate tunnels, vehicular and pedestrian tunnels and stream enclosures. Functions well in all applications, but especially in those with high cover x x

MULTI-PLATE

BridgeCor x Aluminum Structure Plate

Vertical Ellipse 4’-8” x 5’-2” to 25’ x 27’-8”

Culverts, storm sewers, service tunnels, recovery tunnels and stream enclosures. Works well in higher cover applications.

x MULTI-PLATE x Aluminum Structure Plate

Underpass 12’-2” x 11’-0” to 20’-4” x 17’-9”

Offers efficient shape for passage of pedestrians or livestock, vehicular traffic and bicycles with minimal buried invert.

x MULTI-PLATE x Aluminum Structure Plate

Pipe-Arch 6’-1” x 4’-7” to 20’-7” x 13’-2”

Limited headroom. Has hydraulic advantages at low flow levels. Culverts, storm sewer, underpass and stream enclosures.

x MULTI-PLATE x Aluminum Structure Plate

Horizontal Ellipse 7’-4” x 5’-6” to 14’-11” x 11’-2”

Culverts, bridges, low cover applications, wide centered flow, good choice when poor foundations are encountered.

x MULTI-PLATE x Aluminum Structure Plate

Arch (single radius)* 6’ x 1’-10” to 54’-4" x 27’-2”

Low clearance, large waterway opening. Aesthetic shapes and open natural bottoms for environmentally-friendly crossings.

x x

MULTI-PLATE

BridgeCor x Aluminum Structure Plate

Arch (2-radius)* 18’-5” x 8’-4” to 50’-7” x 19’-11”

Low clearance, large waterway opening. Aesthetic shapes and open natural bottoms for environmentally-friendly crossings.

x BridgeCor

Box Culvert 8’-9” x 2’-6” to 40’9” x 15’2”

Very low, wide bridges, culverts and stream enclosures, with limited headroom. Functions well as a fast small-span bridge replacement.

x BridgeCor x Aluminum Box Culvert

Low-Profile Arch 19’-5” x 6’-9” to 45’-0” x 18’-8”

Culvert, storm sewers, low headroom and large opening.

Bridge structures, stream enclosures. Aesthetic shapes and open natural bottoms for environmentally friendly crossings.

x SUPER-SPAN x SUPER-PLATE***

High-Profile 20’-1” x 9’-1” to 35’-4” x 20’-0”

Culverts, storm sewers, bridges, Higher rise, large area opening. Open natural bottoms for environmentally friendly crossings.

x SUPER-SPAN x SUPER-PLATE

Horizontal Ellipse 19’-4” x 12’-9” to 37’-2” x 22’-2”

Larger culverts and bridges. Low headroom, wide-centered flow, good choice when poor foundations are encountered.

x SUPER-SPAN x SUPER-PLATE

Pear-Arch

23’-11” x 23’-4” to

30'-4" x 25'-10" Railroad underpasses or large clearance areas. Open natural bottoms for environmentally friendly crossings. x SUPER-SPAN

Pear 23’-8” x 25’-5” to 29'-11" x 31'-3"

Railroad underpasses or large clearance areas. x SUPER-SPAN

Elliptical/Circular Arch ** 12’ to 102’

Culverts, bridges, tunnels, wetlands crossings, overpass/ underpass, underground containment, wine/cheese cellars and shelters.

CON/SPAN®

BEBO®

(precast concrete)

Vehicular ** spans up to 300’ spans up to 150’

County, city, parks, industrial complexes.

Recreational, overpasses, industrial conveyor, pipe support. x

Steadfast Bridges® Vehicular Truss Big R Bridge® Rolled Girder

* Larger steel sizes are available up through 80-foot spans with external reinforcements in the BridgeCor® product line.

Contact your local Contech representative for more information.

** The design process for these bridge structures is not covered in this document. Contact your local Contech representative for more information.

*** Low-Profile Arch SUPER-PLATE is only available up to 38'-8" x 15'-9".

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Selection of Structure Shape Contech manufactures and supplies structural plate in a wide variety of structure shapes and sizes in both galvanized steel and aluminum alloy. The large selection of structure types ensures that a designer will be able to select the optimum structure for virtually any application from low cover situations to extreme cover heights and from pedestrian underpasses to grade separations for airport runways or railroad passages.

The structures listed on page 4 are generally configured for use in specific drainage or traffic passage applications.

They are prioritized from top to bottom to ensure the most efficient usage and best economy. For example, a designer should first check to see if a round structure will satisfy the project requirements. If there is inadequate headroom for a round structure, proceed to a pipe-arch, horizontal ellipse, or arch and on to box culverts. If a larger structure is required, consider a SUPER-SPAN or BridgeCor type structure. More detailed structure dimensions and information can be found in later sections of this document.

Following are some tips on structure shape and size selection:

a It is usually best to select a shape that most closely matches the shape of the drainage channel. For example, a deep narrow channel will accept a round structure. horizontal ellipses, low profile arches and box culvert shapes are best suited to relatively wide, shallow channels.

a Determine the end area requirement in square feet for the structure and divide the number by the vertical distance from the streambed to the surface elevation less approximately 1.5’ to 3.0’ for fill cover over the structure. This will somewhat underestimate the approximate minimum span required depending upon the structure shape.

a Identify the most efficient structure in terms of reducing design loads. For box culverts, choose a structure that meets the hydraulic requirements and provides a cover of 3-4 feet. A taller structure which minimizes cover may be less cost-effective than one of similar span with slightly higher cover.

tallest structure feasible to minimize cover. As cover increases, so does gage as well as footing sizes.

l Where fill over the structures is low, choose a structure that maintains the minimum allowable cover.

Additional Considerations

In addition to simple geometric and hydraulic concerns, the designer should consider other parameters that may influence structure type, shape and material including:

• High Cover Applications

For fill heights over 30’, the designer should consider Key-Hole Slot MULTI-PLATE® as discussed on page 16.

• Pipe Structure versus Arch on Footings

In general, a pipe structure with a full invert or buried invert is preferable in terms of cost versus an arch because of the elimination of concrete footings. However, many regulations require natural, undisturbed stream bottoms. In this case, an arch on footings is typically less expensive than a traditional bridge.

• Bearing Capacity

See specific sections in this guide for individual structure types for recommendations on minimum bearing capacity and footing designs. Pipe arch design should include considerations of applied corner bearing pressure.

• Flow Characteristics

If flow is to be particularly abrasive, the designer should consider a natural invert (arch or buried invert), heavier invert plates, an aluminum structure, or applying a paved invert to aid in the long-term durability of the structure.

• Corrosive Soils

Analyze structure life projections based upon the CALTRANS/ AISI method. If design life is not met using galvanized steel, consider asphalt coating the steel, adding a concrete field paved invert or using aluminum as an alternate. See page 11 for recommendations for protection from de-icing salts.

• Corrosive Effluents

Analyze structure invert life projections based upon the CALTRANS/AISI method. If design life is not met using galvanized steel, consider either heavier gage invert plates, paved invert, natural invert, or aluminum. In particularly corrosive situations an arch on elevated footing walls (pedestal walls) may be the best solution.

Design Guide

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Scour

If scour is a concern, a pipe structure, especially with a buried invert, may be more desirable than an arch. The invert eliminates footings subject to scour. Also, arches with partially buried structure legs (and footings) may satisfy scour depth.

Often, when an arch on footings must be used, protecting the footings, may be more cost effective than installing deeper footings. Products to consider for this type of protection include rip-rap, sheet piling, or as a permanent erosion control option, Armortec hard armor solutions. Scour analysis is outside the scope of this guide.

FHWA Hydraulic Engineering Publication HEC-18 outlines the design for scour. FHWA Hydraulic Engineering Publication HEC-23 outlines the design procedures for scour counter measures.

Clearance Box Requirements

The following describes the process of selecting a structure with sufficient clearance for the passage of vehicular or pedestrian traffic.

It should be noted that the dimensions of finished corrugated metal structures may differ from the nominal dimensions described in literature. For instance, taller single radius arches may peak slightly during backfilling, which may infringe upon the required clearance box.

If clearance tolerance is critical, it is recommended that a slightly larger structure be selected or that the structure shape be monitored during erection and backfilling.

Proper control of compaction and the use of high quality granular backfill material will minimize structure movement during backfilling. Contact your Contech representative for assistance regarding monitoring and the use of particular shapes.

MULTI-PLATE® and Aluminum Structural Plate vertical ellipses and underpass shapes are configured specifically for vehicular and pedestrian traffic. The structure's invert is often paved to provide a smooth surface. See page 12 for details.

While arch structures often appear to be the best choice for many applications, the same shape in a round or elliptical shape may be more economical due to the elimination of footings. For example, a round structure or horizontal ellipse with the invert buried and/or paved are often used in lieu of an arch for grade separation structures.

Horizontal ellipse SUPER-SPAN™

Protect footings from scour with Armortec® hard armor solution ica l D e sig n Ste p s

Designing For Service Life After a structure shape, size, and gage have been selected, the designer should perform an analysis of the possible environmental effects on the structure's long-term life cycle.

This may lead the designer to modify the structure's material, structure type, coating, or additional invert protection.

A structure's life cycle can be affected by the corrosive action of the backfill in contact with the outside of a structure or more commonly by the corrosive and abrasive action of the flow in the invert of the structure. The design life analysis of the structure should include a check for both water side and soil side environments to determine which is most critical or which governs structure life.

Resistivity pH Resistivity Hardness

The choice of material or structure type can be extremely important to service life. For example, if it is determined that water and bedload flowing through a structure is projected to reduce the life cycle of the invert through abrasive or corrosive action, an arch may be used with a natural invert or the invert may be buried or paved.

Corrosion Studies for Metal Structures

Galvanized steel structural plate has been used in the United States since 1931. Aluminum Structural Plate has been in use since the early 1960’s. Tens of thousands of structures are in use in a wide variety of applications and environments. This wealth of experience provides unsurpassed “in-the-ground” knowledge of performance.

Several rational methods exist for determination of the effects of corrosion upon galvanized steel and aluminum drainage structures. Numerous federal agencies, including the Federal Highway Administration and U.S. Army Corps of Engineers as well as a large number of state departments of transportation, have published guidelines on the subject.

All have valuable information pertinent to possible corrosive effects on both steel and aluminum materials.

Galvanized Steel MULTI-PLATE®

With regard to the durability of galvanized steel MULTI-PLATE, this design guide will outline the guidelines established by the California Department of Transportation (CALTRANS).

The CALTRANS design method originated from a study that inspected over 7,000 galvanized steel corrugated metal pipe (CMP) drainage structures throughout the state of California.

Through this field study they were able to develop a reliable method for predicting the service life of smaller diameter corrugated galvanized steel pipes. The data collected reflected the combined effects of corrosion and a wide range of abrasive levels. The conclusion of the CALTRANS study defined the end of the structure life to coincide with the first perforation (or approximately 12% metal loss) in the invert of culverts that have received no special maintenance.

The service life of 2 oz. per square foot of zinc-coated galvanized CMP is determined by using the CALTRANS chart for estimating invert life (see page 8). This chart predicts a variable service life based on pH and resistivity of water and soil and has been the industry standard for many years. The results included the combined effects of soil-side and interior corrosion, as well as the average effects of abrasion. For pipes where the pH was greater than 7.3, soil-side corrosion controlled and life was predicted by resistivity. For pipes where pH was less than 7.3, the interior invert corrosion generally controlled and both pH and resistivity were important.

It is important to note, the consequences of small perforations are minimal in gravity flow pipe systems, such as most storm sewers and larger culverts, and may not accurately reflect the estimated service life outlined by CALTRANS. Because of this fact, the original CALTRANS curves have been converted to average service life curves using data on weight loss and pitting in bare steel developed by National Institute of Standards and Technology. Using this information, the American Iron and Steel Institute (AISI) developed a durability chart using the end of an average effective service life to be estimated at approximately a 25% metal loss in the invert. The AISI chart can be found at NCSPA.org.

In addition, the structural plate covered in this design guide utilizes a 3 oz. per square foot of zinc coating and uses heavier gage material as part of the structural design. This is a 50% increase in additional barrier coating and adds additional base metal thickness that was not investigated in the original CALTRANS study. These two additional key factors will provide a longer service life than predicted in these charts.

If the designer has site specific knowledge and understands the key design parameters, the AISI method may be more applicable in the pipe service life design. Many state DOT’s find the CALTRANS method to be a conservative estimate of the average observed service life of galvanized steel structures in their states.

Steel and Alum inum

Design Guide

Typical Design Steps

Figure 1. CA

LTR

A N

S Chart For Estim ating A verage Invert Life For Plain G alvanized Culverts

MINIMUM RESISTIVITY (R) ohm cm

A V

ER

A

G

E IN

V

ER

T LIFE–YEA

R

S 1 G

A G

E G A

LV

A

N

IZ

ED

STEEL SH

EET

Thickness 0.052 0.064 0.079 0.109 0.138 0.168 0.188 0.218 0.249 0.280

Gage 18 16 14 12 10 8 7 5 3 1

Factor 1.0 1.3 1.6 2.2 2.8 3.4 3.71 4.31 4.91 5.51

1 Factors extrapolated ica l D e sig n Ste p s

72-Year-Old Steel Structural Plate Pipe Arch Installed c. 1940 | Inspected in 2012

Aluminum Structural Plate

Studies similar to those conducted by CALTRANS have been performed upon a large number of Aluminum Structural Plate installations for the same purpose although none have produced a mathematical model like that for galvanized steel. Aluminum loss rates have been so low as to preclude a reliable model.

Aluminum alloy reacts much differently than galvanized steel when in contact with air, soil, and water. Instead of zinc/steel system of galvanic protection, aluminum resists corrosion by a passive formation of a very tenacious aluminum-oxide layer on its surface. This oxide layer has been shown in field and laboratory observation to be stable in an environment of pH between 4 and 9 and resistivity greater than 500 ohm-cm. Within this range, corrosion rates are minimal and prediction of service life is a matter of assigning a pit rate based upon laboratory testing. Conservatively, a pit rate based on 0.001”/yr may be used.

In this case:

0.100” thick plate 0.001”/yr = 100 yrs design life.

Actual field observations of aluminum alloy pipe (ALCLAD) and Aluminum Structural Plate support this estimation.

In tidal brackish and saltwater environments, Aluminum Structural Plate will perform well if backfilled with free-draining material. The pH and resistivity requirements outlined previously must also be met. Sea water normally exhibits a pH range of 7.5 through 8.0 and resistivity that is less than 100/ohm-cm, but given the neutral pH and a free draining backfill, Aluminum Structural Plate still performs well.

For more detailed information on the subject of corrosion or copies of the referenced documents or guidelines, contact your Contech representative.

Although a gravity flow drainage structure of any kind functions properly well beyond the occurrence of the first perforation, the use of the CALTRANS method best illustrates the variety of environmental conditions found throughout the country.

An important factor when choosing a design method, either CALTRANS or AISI, is knowledge of the structure backfill type. A structure backfilled with very fine material may be affected by the loss of this material through perforations. Thus, the CALTRANS method may be valid. If the required backfill is more granular, which is usually the case with plate structures, then first perforation is probably inconsequential and, therefore, the AISI method would be more appropriate.

For added service life with steel structures, an optional polymer coating may be applied to the plates. Please refer to page 27 for specification information.

Hard or Soft Water Considerations

The designer should note that other factors will affect the rate of metal loss. The primary factor is the presence of dissolved salts such as CaCO3 and MgCO3. Total hardness is a measure of the level of dissolved salts and defined water runoff as hard or soft water.

Hardness levels greater than 300 mg/L indicate dissolved salts (hard water) of a level that will cause the formation of a mineral “scale” on the galvanized surface that will provide excellent protection and increased service life in the absence of abrasion.

Inspections have shown 50-year-old structures with mineral scale and pristine metal conditions beneath.

Hardness levels below 300 mg/L warrant further consideration by the designer and the possible use of coatings, invert protection/paving or aluminum.

In general, the recommended environmental range for use of galvanized steel structural plate that will provide a minimum service life of 50 years is a pH from 6 through 10, and a resistivity of 2,000 ohm-cm through 10,000 ohm-cm**

* Values greater than 10,000 ohm-cm for water side resistivity may indicate low level of dissolved salts (soft water). Water hardness should be tested. Additional protection may be required to meet the required design service life.

Design Guide

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Abrasion Considerations

The potential for metal loss in the invert of a drainage structure due to abrasive flows is often overlooked by designers, and its effects are often mistaken for corrosion.

Environments conducive to abrasive flows are well defined but due to the periodic nature of this event, it is easy to miss.

Three factors must combine to cause invert abrasion:

Examples of abrasive materials include but are not limited to sands, gravels, and stone. The designer should not underestimate the abrasive action of sand transported in sustained flows. When flow velocities reach approximately 5-6 feet-per-second, sand and gravels can become mobile or suspended.

Most commonly, abrasive bedloads remove protective mineral scale and produce oxidation on galvanized steel which will accelerate corrosion. Upstream stilling basins that allow abrasive particles to settle or drop out prior to entering the structure can be very effective in extending the service life.

Guidelines for abrasion levels are excerpted from the FHWA Memorandum on Design Guidance and Specification Changes for Drainage Pipe Alternative Selection and are shown on the next page.

Both of these factors, velocity and abrasiveness, may be present at a particular site. However, if the flow necessary to carry the bedload occurs only a few times during the life of the structure, abrasion may not be a concern. The designer should refer to the 2- or 5-year event velocity and then use this to decide if abrasion is a valid concern.

Should abrasion be determined to be a limiting factor in structure life, several solutions are available to the designer.

These solutions include:

Aluminum performs better than galvanized steel when subjected to abrasion. In some cases, the formation of the oxidized steel layer (in hard water) is removed by abrasion, exposing the galvanized coating beneath. After years of abrasion have taken place, the protective galvanized coating is abraded away and corrosion of the bare steel begins.

This corrosion/abrasion cycle continues for the life of the structure.

Aluminum may lose its oxide layer when abraded away but it quickly reforms at low flows, therefore limiting corrosion.

Aluminum does not have a protective coating to lose after years of abrasive flow.

This is not meant to suggest that Aluminum Structural Plate should be used in heavily abrasive environments. However, its performance can be expected to be superior to plain galvanized steel.

FHWA Memorandum on Design Guidance and Specification Changes for Drainage Pipe Alternative Selection

The durability and service life of a drainage pipe after installation is directly related to the environmental conditions encountered at the site and the type of materials and coatings from which the culvert was fabricated. Two principal causes of early failure in drainage pipe materials are corrosion and abrasion. The environmental damage caused by corrosion and abrasion can be delayed by the type of materials, coatings and invert protection.

It is the Federal Lands Highway (FLH) policy to specify alternative drainage pipe materials on projects where feasible and to comply with the provisions of the Federal-Aid Policy Guide Section 611.411(d). All permanent drainage pipe installations shall be designed for a minimum of 50 years with a maintenance-free service life. A shorter service life may be used for temporary installations, and a longer service life may be considered in unusual situations.

All suitable pipe materials, including reinforced concrete, steel, aluminum and plastic pipe shall be considered as alternatives on FLH projects. The portion of this pipe selection criteria covering metal pipe complies with the guidance contained in Federal Highway Administration (FHWA) Technical Advisory T 5040.12 dated October 22, 1979, and incorporates information contained in FHWA- FLP-91-006, Durability of Special Coatings for Corrugated Steel Pipe.

Bay of Fundy | Robinston, ME 52-Year-Old Aluminum Structural Plate Installed in 1966 | Inspected in 2018 ica l D e sig n Ste p s

Abrasion: An estimate of the potential for abrasion is required at each pipe location in order to determine the need for invert protection. Four levels of abrasion are referred to in the FHWA guidelines and the following guidelines are established for each level:

• Level 1: Nonabrasive conditions exist in areas of no bed load and very low velocities. This is the condition assumed for the soil side of drainage pipes.

• Level 2: Low abrasive conditions exist in areas of minor bed loads of sand and velocities of 5 feet per second (1.5 meters per second) or less.

• Level 3: Moderate abrasive conditions exist in areas of moderate bed loads of sand and gravel and velocities between 5 and 15 fps (1.5 m/s and 4.5 m/s).

• Level 4: Severe abrasive conditions exist in areas of heavy bed loads of sand, gravel, and rock and velocities exceeding 15 fps (4.5 m/s).

These definitions of abrasion levels are intended as guidance to help the designer consider the impacts of bedload wear on the invert of pipe materials. Sampling of the streambed materials is not required, but visual examination and documentation of the size of the materials in the streambed and the average slope of the channel will give the designer guidance on the expected level of abrasion. Where existing culverts are in place in the same drainage area, the existing conditions of inverts can be used as guidance. The expected stream velocity should be based upon a typical flow and not a 10- or 50-year design flood.

Corrosion: Alkalinity/Acidity (pH) and Resistivity— Determinations of pH and resistivity are required at each pipe location in order to specify pipe materials capable of providing a maintenance free service life. The samples shall be taken in accordance with the procedures described in AASHTO T 288 and T 289. Samples should be taken from both the soil and water side environments to ensure that the most severe environmental conditions are selected for determining the service life of the drainage pipe. Soil samples should be representative of backfill material anticipated at the drainage site. Avoid taking water samples during flood flows or for two days following flood flows to insure more typical readings. In locations where streams are dry for much of the year, water samples may not be possible or necessary. In areas of known uniform pH and resistivity readings, a random sampling plan may be developed to obtain the needed information.

In corrosive soil conditions where water side corrosion is not a factor, consider specifying less corrosive backfill material to modify the soil side environment. The advantages of properly specified backfill should be taken into account in making alternative pipe materials selections in situations where soil side conditions control.

Adjustments for Abrasion

Once the minimum structural gage is selected and the service life requirement is compared to “The CALTRANS Chart for Estimating Average Invert Life” (on page 8) adjustments should be made based on the abrasion potential of the site.

Steel

At non-abrasive or low abrasive sites, no additional protection is needed. At sites that are moderately abrasive, increase the thickness of the material by one standard thickness or add invert protection like a concrete paved invert. At severely abrasive sites, increase the thickness of the material by one standard thickness and add a concrete paved invert.

Aluminum

At non-abrasive, low abrasive or moderately abrasive sites, no additional protection is needed. At severely abrasive sites, increase the thickness of the material by one standard thickness and add a concrete paved invert.

Additional Service Life Considerations

Dissimilar Metals

Metals with a substantial difference in electrical potential should be insulated from each other. Electrical potential may be established by referring to the electromotive scale.

The only significant concern with regard to structural plate is the use of “black” steel in conjunction with aluminum.

Black steel should not be in contact with aluminum. Hot Dipped Galvanized steel is compatible with Aluminum Structural Plate.

Concrete or Grout in Contact with Aluminum

During the relatively short period while concrete cures, minor etching (<0.001”) of the surface of the plate will occur. If the designer is concerned with cosmetic etching of the aluminum, the surface may be coated with asphalt or primer paint.

De-icing Salts

The potential for use of de-icing salts on roadway surfaces above structural plate must be addressed during the design phase. Calcium chloride and magnesium chloride as well as other de-icing materials can cause corrosion of galvanized steel and aluminum.

It is recommended that the designer consider the use of either an asphalt coating on the exterior of the structure or a HDPE membrane over the structure. Details for each of these solutions are presented on the following pages.

In addition, impermeable clay layers above the select backfill have been used to shed water from the crown of the structure.

Design Guide

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HDPE Membrane Protection from De-Icing Salts

30 mil (minimum thickness) HDPE membrane draped over structures & sloped to drain water away from structure. The length of the membrane should cover the top of the structure.

Structural Plate Detail for Concrete Paved Invert

HDPE Membrane Protection Detail for Structural Plate

12” ica l D e sig n Ste p s

Live Loads

Live loads reaching the structure are more complicated to determine. AASHTO has prepared a very comprehensive method for determination of the loads reaching the corrugated metal structure.

Live loads consist of traffic loads applied to the surface or roadway above the structure. These loads also consider the effect of impact loads. Live loads reaching the structure diminish with increasing heights of cover.

Overall, this manual considers HL-93 highway loads.

Other highway loads, such as HS-20 and HS-25, can be addressed. Cooper (E-80) railroad loads are addressed in the Amercian Railroad Engineering and Maintenance-of- Way Association (AREMA) specification which is similar to the procedure outlined. Airport loading and off-highway loads such as mining equipment are special loading conditions. For additional design support, contact your local Contech representative.

AASHTO Design Load and Redundancy Factors

The AASHTO design load factors that are required to perform the calculation are summarized in the table below.

Structural Plate Design

MULTI-PLATE® and Aluminum Structural Plate Determination of Metal Thickness

According to the American Association of State Highway and Transportation Officials (AASHTO) LRFD Design Specification, Section 12.2 for corrugated metal plate structures “…become part of a composite system comprised of the metal pipe section and the soil envelope, both of which contribute to the structural behavior of the system.”

Design methods for corrugated metal plate structures are well established and provide the designer with straightforward, conservative procedures. Current AASHTO design procedures also address foundations, backfill, and end treatments. (See page 27 for listing of all applicable design specifications.)

The basic plate structural design process for the determination of the structure gage consists of:

1. Determine the backfill soil density adjacent to and above the metal structure.

2. Calculate the design pressure applied by the soil column and live load.

for wall yielding and buckling using the corrugated section properties.

5. Check for sufficient bolted longitudinal seam strength between plates.

6. Check for minimum stiffness required for proper handling, assembly, and installation.

7. Apply appropriate LRFD factors.

Dead Loads

Dead loads are those developed by the soil fill above the structure plus those of any stationary surcharge loads that can influence the structure. Dead loads are calculated by multiplying the soil density by the height of cover and applicable load and redudancy factors. The unit weight of soil is assumed to be 120 pcf unless otherwise stated.

TABLE 1.

AASHTO DESIGN LOAD AND REDUNDANCY FACTORS FOR MULTI-PLATE & ALSP

Symbol Term Value AASHTO

Φw Wall Area and Buckling 1.00 (Table 12.5.5-1)

ΦSS Seam Strength 0.67 (Table 12.5.5-1)

ΦBP Backfill Bearing Resistance 1.00 (Table 12.5.5-1) ηEV Redundancy Factor 1.05 (1.3.4, 12.5.4) ηLL Redundancy Factor 1.00 (1.3.4, 12.5.4)

ϒEV Dead Load Factor 1.95 (Table 3.4.1-2)

ϒLL Live Load Factor 1.75 (Table 3.4.1-1)

For additional information on the methodology for developing these load pressures or AASHTO, AISI, and AREMA tables, contact your local Contech representative.

Design Guide

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24’-0” diameter steel MULTI-PLATE® designed for 60 feet of fill owned by VDOT in Dryden, Virginia

Structural Plate Design - Seam Strength

When the design analysis shows the seam strength of a structure is the limiting factor, which can occur when fill heights become significant, the design engineer can increase the material thickness to add seam strength for a particular design.

TABLE 2.

ULTIMATE SEAM STRENGTH

OF BOLTED 6" X 2" STEEL STRUCTURAL PLATE LONGITUDINAL SEAMS

IN POUNDS PER FT OF SEAM

Gage Thickness (Inches)

6” x 2” Corrugation

4 Bolts Per Ft.

6 Bolts Per Ft.

8 Bolts Per Ft.

12 0.111 42,000 10 0.140 62,000 8 0.170 81,000 7 0.188 93,000 5 0.218 112,000 3 0.249 132,000 1 0.280 144,000 180,000 194,000

5/16 0.318 235,000 3/8 0.380 285,000

Notes:

1. Bolts used are 3/4” diameter – high strength bolts with suitable nuts, meeting ASTM A449.

2. Bolts and nuts also used for connecting arch plates to receiving angles and structural reinforcement to structural plates.

3. 5/16 and 3/8 require 7/8” fasteners.

TABLE 3.

ULTIMATE SEAM STRENGTH

OF BOLTED 15" X 5½" STEEL STRUCTURAL PLATE LONGITUDINAL SEAMS

IN POUNDS PER FT OF SEAM

Gage Thickness (Inches)

15” x 5½” Corrugation

30" long plates

45" long plates

8 0.170 109,000 89,000 7 0.188 126,000 101,000 5 0.218 155,000 124,000 3 0.249 181,000 160,000 1 0.280 187,000 162,000

5/16 0.318 231,000 n/a 3/8 0.380 252,000 n/a

Notes:

1. Bolts used are 3/4” diameter – high strength bolts with suitable nuts, meeting ASTM A449.

2. Bolts and nuts also used for connecting arch plates to receiving angles and structural reinforcement to structural plates.

3. 5/16 and 3/8 require 7/8” fasteners.

4. The values listed above are per ASTM A796.

TABLE 4.

ULTIMATE SEAM STRENGTH

OF BOLTED ALUMINUM STRUCTURAL PLATE LONGITUDINAL SEAMS

IN POUNDS PER FT OF SEAM

Thickness (Inches) Ultimate Seam Strength

0.100 28,000

0.125 41,000

0.150 54,100

0.175 63,700

0.200 73,400

0.225 83,200

0.250 93,100

Note: Bolts used are 3/4” diameter – high strength bolts with suitable nuts, meeting ASTM A307/A449.

See page 29 for MULTI-PLATE standard detail.

See page 48 for ALSP standard plate detail.

See page 89 for BridgeCor standard plate detail.

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Section Properties

TABLE 5.

STEEL CONDUITS

Gage Thickness (Inches)

6” x 2” Corrugations

Area of Section

As

Radius of

Gyration r

Section Modulus

S

Moment of Inertia

I

Sq. In./Ft. (Inches) In.3/In. In.4/In.

12 0.111 1.556 0.682 0.0574 0.0604

10 0.140 2.003 0.684 0.0733 0.0781

8 0.170 2.449 0.686 0.0888 0.0962

7 0.188 2.739 0.688 0.0989 0.1080

5 0.218 3.199 0.690 0.1147 0.1269

3 0.249 3.650 0.692 0.1302 0.1462

1 0.280 4.119 0.695 0.1458 0.1658

5/16 0.318 4.671 0.698 0.1640 0.1900

3/8 0.380 5.613 0.704 0.1950 0.2320

TABLE 6.

ALUMINUM CONDUITS

Thickness (Inches)

9” x 2 1/2” Corrugations

Area of Section

As

Radius of

Gyration r

Section Modulus

S

Moment of Inertia

I

Sq. In./Ft. (Inches) In.3/In. In.4/In.

0.100 1.404 0.8438 0.767 0.0836

0.125 1.750 0.8444 0.951 0.1040

0.150 2.100 0.8449 1.131 0.1249

0.175 2.449 0.8454 1.309 0.1459

0.200 2.799 0.8460 1.484 0.1670

0.225 3.149 0.8468 1.657 0.1882

0.250 3.501 0.8473 1.828 0.2094

TABLE 7.

MECHANICAL PROPERTIES FOR

STEEL STRUCTURAL PLATE MATERIAL

fu Minimum

Tensile Strength (psi) fy Minimum

Yield Point (psi)

Em Modulus of Elasticity (psi)

45,000 33,000 29 x 106

Note: Material requirements based on AASHTO M 167

TABLE 8.

MECHANICAL PROPERTIES FOR

ALUMINUM STRUCTURAL PLATE MATERIAL

Thickness (Inches) fu Minimum

Tensile Strength (psi) fy Minimum

Yield Point (psi)

Em Modulus of Elasticity (psi)

0.100 to 0.175 35,000 24,000 10 x 106

0.200 to 0.250 34,000 24,000 10 x 106

Note: Material requirements based on AASHTO M 219, Alloy 5052

“The Chief” a 5,000,000 lb. drag line over steel SUPER-SPAN™ at Peabody Coal in Zanesville, Ohio

Design Guide

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Key-Hole Slot MULTI-PLATE® Structures Under High Fill

MULTI-PLATE can be designed to handle high fill heights greater than 30' using Key-Hole Slot MULTI-PLATE. The slot provides self-indexing, controlled-yield bolted joints along a Key-Hole Slote MULTI-PLATE structure's longitudinal seams.

These joints yield under compressive loads and thereby reduce the circumference of the structure, so that much of the load is carried by the soil instead of by the steel structure.

In effect, the Key-Hole Slot MULTI-PLATE becomes a yielding-ring structure. The design allows the seams to slip under load without any loss in ultimate seam strength. (See Figure 2).

Soil Arching

The compressive loads reach a level which varies by gage, causing the 3/4-inch bolt shank to wedge into the 5/8-inch slot.

This controlled yielding action in the structure seams decreases the structure circumference, promoting a high degree of soil arching over the structure. For these deep cover applications, A-1-a backfill per AASHTO M 145 is required as backfill for these types of flexible structures.

While specific design criteria must be applied to any project, the use of Key-Hole Slot MULTI-PLATE versus standard MULTI-PLATE can decrease the gage (material thickness) by one to three gages. A CALTRANS deep burial study compared standard MULTI-PLATE to Key-Hole Slot MULTI-PLATE and found that the average thrust created at the springline level of the Key-Hole Slot structure was approximately 50% of standard structure.

This reduction in thrust in turn reduces the required seam strength, and therefore, the structure wall gage or thickness.

The designer is urged to contact a Contech representative for additional information on Key–Hole Slot MULTI-PLATE.

Figure 2. Key-Hole Slot MULTI-PLATE® at work

Along the Eastern Transportation Corridor in Orange County, California, this Key-Hole Slot MULTI-PLATE® structure was designed for the 115 ft. of cover.

Lapped Joint - Fully Slipped (1" Into Slots) Inside View

Lapped Joint - No Load Inside View

Bottom Plate

Bottom Plate Bottom Plate

¾” Bolt ¾” Bolt

Top Plate

Top Plate

Lo ad

Lo ad

Top Plate

Bottom Plate

Bottom Plate Bottom Plate

¾” Bolt ¾” Bolt

Top Plate

Top Plate

Lo ad

Lo ad

Top Plate ica l D e sig n Ste p s

Alumnium Box Culvert installation

Aluminum Box Culvert multi-cell installation

Aluminum Box Culvert Design

The structural design of an Aluminum Box Culvert (ALBC) does not follow the processes previously discussed in this guide. Due to the shape of the box culvert, the “ring compression” method used to quantify design pressures does not apply. The relatively large radius crowns are subject to high moment forces. Therefore, a separate method is used to ensure that the Aluminum Box Culvert can support both the earth loads and the live loads applied to these structures under relatively shallow fills. Primarily, the design procedure quantifies the capacity of the corrugated aluminum shell and reinforcing ribs to resist bending moments.

MpH (Mp)

(Mp)

MpC

Due to the indeterminate nature of the structural elements, finite element analysis was developed to evaluate the plastic moment capacity of the structure. The design requirements for Aluminum Box Culverts are contained in the AASHTO Highway Bridge Design Manual Section 12.8.

Contech Engineered Solutions has also generated height of cover tables that meet the requirements of AASHTO for HL-93, HS-20, and HS-25 live loads that supply the plate gages and reinforcing ribs necessary for a given height of cover. These values are contained in the Aluminum Box Culvert section of this manual. Note that the allowable range of minimum and maximum cover heights is limited for aluminum box culverts. Additionally, live load is restricted to standard highway vehicles. Heavy construction loads and other heavy live load traffic are not permitted over these structures without special provisions.

Design Guide

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Thrust Beam

The primary differences in long span design procedures and standard plate structures design procedures are:

l Design checks for buckling and flexibility are not applied because of special features not found in other Structural Plate structures and also because of the use of high quality backfill and shape monitoring during backfill.

l Special features such as longitudinal thrust beams are incorporated to assist in the ability of the structure to transfer load to the surrounding soil envelope. Thrust beams also work to isolate the top arc, diminishing the need for a buckling analysis.

l Gage of the top plates and minimum cover are determined by the top radius (see Table 9)

than 2.0 and less than or equal to 4.4

Gage or thickness for SUPER-SPAN is a function of the structure's top radius and the live and dead loads. Table 9 below provides the recommended gages and minimum covers for SUPER-SPAN. The designer should also note that Contech Engineered Solutions provides a Shape Control Technician as a condition of the sale of a SUPER-SPAN or SUPER-PLATE. The Shape Control Technician will be on-site until the select backfill reaches the minimum height of cover required to ensure proper finished structure shape.

Aluminum SUPER-PLATE long spans are available in most of the same sizes and shapes as steel SUPER-SPAN.

Further information is available in the SUPER-SPAN and SUPER-PLATE section of this design guide and technical guidelines contained in this brochure.

SUPER-SPAN™ and SUPER-PLATE® Design Design of SUPER-SPAN and SUPER-PLATE (Long Span) structures follow AASHTO Section 12.7.

SUPER-SPAN and SUPER-PLATE feature relatively large radius or flatter curvature in the top or sides (larger than standard structural plate designs). These shapes include:

Horizontal Ellipse

Low Profile Arch

High Profile Arch

Pear Shape Pear Arch

SUPER-SPAN structure near Cumming, Georgia

TABLE 9.

MINIMUM THICKNESS — MININUM COVER TABLE (HL-93, H-20, HS-20, H-25, HS-25 LIVE LOAD)

Wall Thickness (Inches)

Top Radius 0.111 0.140 0.170 or 0.188 0.218 0.249 0.280

RT Ft. (12 Ga.) (10 Ga.) (8 or 7 Ga.) (5 Ga.) (3 Ga.) (1 Ga.)

15’ 2.5’ 2.5’ 2.5’ 2.0’ 2.0’ 2.0’

15’-17’ 3.0’ 3.0’ 2.5’ 2.0’ 2.0’

17’-20’ 3.0’ 2.5’ 2.5’ 2.5’

20’-23’ 3.0’ 3.0’ 3.0’

23’-25’ 4.0’ 4.0’

For additional information regarding this table, refer to notes on page 81. Contact a Contech representative for Pear and Pear-Arch shapes.

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To properly analyze these parameters using finite element analysis it is important to have a geotechnical report for each specific bridge location. This information will allow the designer to optimize both the gage of the steel and the limits of the structural backfill adjacent to the BridgeCor structure.

This design procedure is more comprehensive than a typical ring compression design for MULTI-PLATE structures. Therefore, it will require additional effort to properly evaluate a BridgeCor solution for any application. This additional planning is critical to a successful project.

BridgeCor Monitoring

Due to the potential large sizes of BridgeCor structures and the information outlined in AASHTO Specification Section 26

– Metal Culverts, it is a requirement to monitor the shape of the structure during the backfill process. Depending on the size and complexity of a structure, guidelines have been established to determine what level of monitoring will be required on all projects. There are four levels of monitoring outlined for BridgeCor. These levels range from a preconstruction meeting with a contractor to a full monitoring program similar to the process outlined for a SUPER-SPAN structure. Contact your local Contech representative for additional information.

BridgeCor® Design The design procedure for BridgeCor is outlined in AASHTO LRFD Section 12.8.9 - Deep Corrugated Structural Plate Structures. These structures are designed as long-span culverts but must also meet provisions for flexure and general buckling.

BridgeCor structures can be made in multiple shapes and sizes to meet site specific project requirements.

Structures designed under this specification must be analyzed by accepted finite element analysis.