Trilateral_Design_and_Test_Code_for_Military_Bridging_and_Gap-Crossing_Equipment.doc

TRILATERAL DESIGN AND TEST CODE

FOR MILITARY BRIDGING AND

GAP-CROSSING EQUIPMENT

(Amended - May 2005)

AGREED TO BY:

GERMANY

UNITED KINGDOM

UNITED STATES OF AMERICA

PUBLISHED IN THE UNITED STATES

January 2005

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Design and Analysis Group National RepresentativesPRIVATE

Mr. Johannes Kluck

Telephone:

Bundesamt für Wehrtechnik und Beschaffung K 54

0-11-49-261-6363 Ferdinand-Sauerbruch-Strasse 1

Fax:

56073 Koblenz

0-11-49-261-400-6332

Germany

Email:

Johannes kluck@bwb.org

Dr. Richard Connor

Technical Leader Gap Crossing

0-11-441-202-490283 QinetiQ

Bailey Drive

0-11-441-202-471705 Christchurch

Dorset, BH23 2BN rcconnor@qinetiq.com United Kingdom Chairman

Mr. Brian K. Hornbeck

US Army Tank-automotive & Armaments Command

0-11-01-586-574-5608

ATTN: AMSRD-TAR-E/BRDG MS 21

6501 E. 11 Mile Rd.

0-11-01-586-574-7944

Warren, MI 48397-5000

United States of America brian.hornbeck@us.army.mil

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CONTENTSPRIVATE

Section

Title

Page

FOREWORD

ix

I

GENERAL

1.1 Introduction

1.2 Scope and Field of Application

1.3 References

II

DEFINITIONS AND SYMBOLS

2.1 Definitions

2.2 Symbols

2.3 Conversion Factors

III

MATERIALS

3.1 General

3.2 Material Listing

3.3 Preliminary Working Stresses

3.4 Data required for Selected Materials

3.5 Data Required for Selected Metals

3.6 Data Required for Selected Composites

3.7 Data Required for Selected Adhesives

IV

DESIGN PARAMETERS

4.1 General

4.2 Clear-Span Bridge and General Parameters

4.3 Combination Bridging

4.4 Piers

4.5 Floating Bridges and Rafts

4.6 Typical Vehicle Data for Design

4.7 Temperature and Environment V

LOADS AND LOAD COMBINATIONS

5.1 General

5.2 Deflections

5.3 Military Bridge Loads

5.4 Load Combinations CONTENTS (Continued)

VI

SAFETY

6.1 General

6.2 Design Load (P)

6.3 Safety Coefficients and Combined Stresses for Metal

6.4 Safety Coefficients at Working Load (P) for Composites and Adhesives

6.5 Flotation and Stability

6.6 Fatigue Safety Factor

6.7 Safety Against Overturning or Rotation

6.8 Lifting and Anchorage Safety

6.9 Air Transport Safety

VII

FATIGUE

7.1 Scope

7.2 Load Spectrum Parameters

7.3 Fatigue Design Load Range (PFAT)

7.4 Damage Tolerant Design

7.5 Alternative Designs

VIII

TESTING

8.1 General

8.2 User Trials/Performance Tests

8.3 Dual Testing

8.4 Requirement Tests

8.5 Structural Strength Tests

8.6 Trafficking Tests

8.7 Additional Floating Equipment Tests

8.8 Fatigue Tests

8.9 Resonance

IX

AVOIDANCE OF OVERWEIGHT DESIGN

9.1 General

9.2 Prototype Structure

9.3 Fatigue Considerations

9.4 Economic Considerations

9.5 Modification CONTENTS (Continued)

X

ADDITIONAL CONSIDERATIONS FOR COMPOSITE STRUCTURES

10.1 General

10.2 Testing

XI

RELIABILITY, AVAILABILITY, AND MAINTAINABILITY

11.1 General

11.2 Failure Modes, Effects, and Criticality Analysis (FMECA)

11.3 Parts Control and Component Testing

11.4 Stress Derating

11.5 Design Guidelines and Reviews

11.6 Models and Predictions

11.7 Software Development

11.8 Maintenance Concept

11.9 Desirable Measures of Reliability and Maintainability

XII

BRIDGE CROSSING RATING

12.1 General

12.2 Normal Crossing

12.3 Caution Crossing

12.4 Risk Crossing

12.5 Testing

APPENDIXES

APPENDIX A -

METAL DATA SHEETS

A-1

APPENDIX B -

CONVERSION FACTORS

B-1

APPENDIX C -

CHARACTERISTICS OF HYPOTHETICAL VEHICLES USED

FOR THE RATING OF THE mlc OF VEHICLES AND BRIDGES C-1

APPENDIX D -

International Temper Equivalents for Aluminum Alloys D-1

APPENDIX E -

COMPOSITE MATERIALS DATA FORM

E-1

APPENDIX F -

ADHESIVE DATA FORM

F-1

APPENDIX G -

Typical Basic Properties of Fiber-Reinforced

Materials Based on 60% Fiber Volume Fraction

Epoxy Composites G-1

APPENDIX H -

Safety Factors on Required Life n for

Design and Test H-1

CONTENTS (Continued)

APPENDIXES (Continued)

APPENDIX I -

LIMIT STATE DESIGN (LSD) (Provisional) I-1

APPENDIX J -

STANDARDS

J-1 appendix k – rationale (distribution controlled-NOT INCLUDED) K-1

FOREWORDPRIVATE

This Code has been agreed to by Germany (GE), the United Kingdom (UK), and the United States of America (US). The Code was prepared by the Design and Analysis Group for Military Bridging and Gap-Crossing Equipment. It was first published in 1974, and in 1984 it also became Quadripartite Advisory Publication 21.

The following systems of units are used:

SI

(ISO 1000, US ASTM E380, and UK PD 5686)

US Customary

(US NBS Misc. Pub 233)

Where differences exist between United Kingdom English and United States of America English, the United Kingdom English verbiage is enclosed in brackets: { }.

In order to keep this Code up to date or to modify the requirements when justified by research, test results, or mutually agreed user requirements, it is essential that suggested modifications and revisions or comments are submitted to the cognizant representatives of Germany, the United Kingdom, and the United States of America for agreement. This code has been prepared for the design of bridges and launch mechanisms and is not intended for vehicle design.

I. GENERAL

1.1 Introduction.

1.1.1 Bridging and gap-crossing equipment will be designed to meet the user's requirement by applying the necessary loading conditions, design parameters, and testing given in this Code. The Code lists material properties required and gives basic properties for materials generally used. The Code also gives design data for guidance and checking, but the criteria are that the equipment pass the requisite tests, meet the user's requirement, and can be manufactured readily.

1.1.2 Equipment designed and tested in one country in accordance with this Code will be suitable for international acceptance, apart from user or troop trials.

1.2 Scope and Field of Application.

1.2.1 This Code covers loading, design, and testing requirements to be used for the development of military clear-span bridges, piers, floating bridges, rafts, equipment causeways, and erecting and launching structures that are part of the equipment. The Code is used to confirm that equipment will meet the performance specified by the user. The requirements of this Code are to be regarded as the minimum acceptable standards of performance. Requirements for fibrous composite materials and adhesives are included but may not be complete.

1.2.2 If different materials, unusual structures or techniques are used to which some portions of this Code are inappropriate, the engineer is responsible for devising suitable but similar alternative provisions including the specifying and justifying of special tests.

1.3 References.

1.3.1 This Code overrides all other national standards (except those listed below) relating to military bridging and gap-crossing equipment unless such standards are specifically called for by the user. The standards listed below as being valid in addition to the Code should not be regarded as being complete. Additional unforeseen standards that may become relevant in the future should be agreed upon trilaterally.

1.3.2 User's Equipment Requirement: Military Technical and Economy Requirement (FRG); General Staff Requirement (UK); and Operational Requirements Document (US).

1.3.3 NATO STANAG 2021, Military Load Classification of Bridges, Ferries, Rafts and Vehicles.

1.3.4 QSTAGS and STANAGS for standardization of equipment and details.

1.3.5 International Organization for Standardization (ISO) International Standards.

1.3.6 American Society for Testing Materials (ASTM) or similar national standards.

1.3.7 Production Specifications.

1.3.8 A list of standards related to paragraphs of this Code is given in Appendix J - STANDARDS.

1.3.9 DOT/FAA/AR-MMPDS-01, METALLIC MATERIALS PROPERTIES DEVELOPMENT AND STANDARDIZATION.*

II. DEFINITIONS AND SYMBOLS

PRIVATE

2.1 Definitions.

2.1.1 Allowable Stress. The maximum stress allowed caused by the design load, P. The stress derived from the proof, yield, or ultimate stress divided by the appropriate safety factor.

2.1.2 Applied Loads. The loads applied to a structure in addition to the dead load, D, or self-weight.

2.1.3 Availability. A measure of the degree to which an item is in an operable and committable state at the start of a mission when the mission is called for at an unknown (random) time.

2.1.4 Battlefield Day - see Mission Cycle.

2.1.5 Bearing Contact (Hertz) Stress. The compressive stress due to pressure between elastic bodies.

2.1.6 Buckling Stress. The stress due to the critical buckling load causing unstable equilibrium at which a member fails to perform its load-resisting function due to excessive deflection.

2.1.7 Calculated Ultimate Load (UC). The design or working load, P, multiplied by the factor 1.5.

2.1.8 Design Load (P). The appropriate combination of loads which must be sustained by a structure without producing stresses in excess of the allowable/working value. For static test purposes it is the Working Load, P. In the case of the ductile materials, not sensitive to stress concentrations, average stresses on net sections are satisfactory.

2.1.9 Failure. Failure is when any structural or functional damage causes a member or structure to no longer perform as intended and prevents the completion of its mission; either launching, trafficking, or recovery.

2.1.10 Fatigue Design Life. The required life multiplied by a factor which varies according to the type of design adopted and a further factor if a mean stress/number of cycles (S/N) is used instead of the minimum curve.

2.1.11 Fatigue Stress Range. The stress range to cause failure at the fatigue design life.

2.1.12 Impact Factor. The factor applied to an induced static load to give the equivalent induced dynamic load caused by the load's movement.

2.1.13 Maintainability. The ability of an item, under stated conditions of use, to be retained in or restored to a specified condition when maintenance is performed by personnel having specified skill levels and using prescribed procedures and resources.

2.1.14 Minimum Life. The life at a selected stress from an appropriate S/N curve at 97.5% probability of survival.

2.1.15 Mission Cycle. Includes road march, launch/erection of the equipment, vehicle trafficking and equipment use, and retrieval/disassembly of the equipment.

2.1.16 MLC. Military Load Classification.

2.1.17 Pin Bearing Stress. The compression stress normal to the axis of the fasteners (e.g., rivets, bolts, screws) on the projected area of the hole.

2.1.18 Proof Stress. The stress at which a material deviates from the proportionality of stress to strain by a 0.2% strain offset.

2.1.19 Reliability. The probability that an item will perform to its intended function for a specified interval (mission) under stated conditions.

2.1.20 Required Life. The fatigue life stated in the user's requirements.

2.1.21 Rupture Stress. The same as ultimate stress.

2.1.22 Shear Stress. The stress component tangential to the plane in which the forces act.

2.1.23 Slope. Vertical rise or fall over the horizontal distance, usually expressed as a ratio (e.g. 1 in 10).

2.1.24 Span. The design span is the distance between the reaction point of the bank seats at each support of the bridge. The clear span is the gap to be bridged. See Figure 2-1.

2.1.25 Stress Ratio. Stress ratio is defined as equal to the minimum stress divided by the maximum stress.

2.1.26 Test Overload (O). The design or working load, P, multiplied by the factor 1.33.

2.1.27 Test Ultimate Load (U). The maximum test load achieved by the bridge structure or component before sudden failure or instability.

2.1.28 Ultimate Stress. The maximum tensile, compressive, or shear stress a material is capable of sustaining.

2.1.29 Working Load (P). The same as design load, P.

2.1.30 Working Stress. The stress caused by the working load, P. The working stress may not exceed the allowable stress.

2.1.31 Yield Stress. The stress at which a material deviates from the proportionality of stress to strain. This deviation may be expressed as a 0.2% strain offset.

2.2 Symbols. The following symbols are used in this Code:

Ai

- Applied load to structure or component numbered in order of severity, with A1 being the most severe

B

- Braking load from vehicle(s)

D

- Self-weight or dead load including impact during launching

F

- Footwalk loading

KC

- Fracture toughness property for material (under plane stress)

KIC

- Critical stress intensity for cracking (under plane strain)

Kth

- Threshold Stress intensity

M

- Mud load

N

- Number of cycles to failure

O

- Overload

P

- Design load or Working load

PC

- Stability design load of floating bridge or raft components

PFAT

- Fatigue design load range

PTEST

- Applied test load related to actual material properties

Q

- Hydrodynamic load: the resultant of horizontal drag or propulsion and vertical drawdown components

R

- Function of

S

- Snow or ice load

T1, etc.

- Strength parameters determined by test

U

- Ultimate load

UC

- Calculated ultimate load

Us

- Minimum in-plane shear strength

V

- Vehicle load, including appropriate impact and eccentricity

W

- Wind load at appropriate velocity

WP

- Wind pressure at appropriate velocity

XC

- Minimum compressive failure strength of the unidirectional layer parallel to fiber direction

XT

- Minimum tensile failure strength of the unidirectional layer parallel to fiber direction

YC

- Minimum compressive failure strength of the unidirectional layer perpendicular to fiber direction

YT

- Minimum tensile failure strength of the unidirectional layer perpendicular to fiber direction σ1

- Normal stress in fiber direction σ2

- Normal stress perpendicular to the fiber in the plane of the lamina σ3

- In-plane shear stress σs

- Shear stress σt

- Tensile stress σv

- Maximum stress σx

- Stress in x direction σy

- Stress in y direction h

- Height difference between near and far banks n

- Required number of cycles/life pb

- Tracked vehicle ground contact bearing pressure on hard surface v

- Velocity

- Standard deviation Additional symbols are defined in applicable appendixes.

2.3 Conversion Factors. Conversion factors for SI, Metric, and English units are in Appendix B - CONVERSION FACTORS.

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III. MATERIALSPRIVATE

3.1 General. This section gives the material data which should be available to the designer and is required for international standardization. The data should be presented in the form used in Appendixes A - METAL DATA SHEETS, E - Composite Materials DATA FORM, and F - ADHESIVE DATA FORM.

3.2 Material Listing. Appendix A - METAL DATA SHEETS is a list of metals with brief information to assist initial selection. These are not the only metals for consideration. Approximate properties for composites for preferred methods of fabrication are given in Appendix G - TYPICAL BASIC PROPERTIES OF FIBER-REINFORCED MATERIALS BASED ON 60% FIBER VOLUME FRACTION EPOXY COMPOSITES.

3.3 Preliminary Working Stresses. If when a metal is first considered only the 0.2% proof for yield strength is known, the following factors may be used to obtain other working stresses from the working tensile stress:

Compression without buckling = tension

Shear = 0.6 x tension

Bearing = 1.33 x tension

3.4 Data required for Selected Materials.

3.4.1 General. Name and/or number of material with a brief statement of the primary characteristics and any patent or proprietary restrictions.

3.4.2 Application. State what the material is used for and the particular properties that make it desirable.

3.4.3 Physical Properties.

Give density, melting range, and average coefficient of thermal expansion for -18 to 65 °C (0 to 150 °F).

3.4.4 Elastic Constants. Give at 20 °C (68 °F) the Modulus of Elasticity, in tension and compression, and Poisson's ratio. Orthotropic properties should be given to consider the effect of grain orientation. Variances of more than 5% at 38 °C (100 °F) should be noted.

3.4.5 Fabrication Recommendations. List any special recommendations for working with the material.

3.4.6 Ballistic Damage. It should be shown that any material or construction is satisfactory with respect to ballistic damage. An assessment may be made on the basis of impact tests, fracture toughness, notch tensile/compression tests, drop tests, and field shooting trials followed by test loading.

3.5 Data Required for Selected Metals.

3.5.1 Physical Condition Designation. List and define all common heat-treatment designations.

3.5.2 Chemical Composition. Give the maximum and minimum allowable percentage by weight of alloying elements and the maximum allowable percentage by weight of contaminating elements.

3.5.3 Mechanical Properties. Minimum properties will be given for the parent metal and, if they are different, for welds, Heat Affected Zones (HAZ), and, if applicable, for differently worked forms. Parent-metal properties will be given for the longitudinal direction, in the rolling or extrusion direction, and, if they differ, for the long-transverse and short-transverse directions as well as for various thicknesses. In general, ultimate strength, yield strength, and elongation are guaranteed; however, other mechanical properties must be established and are minimum properties which can be expected but are not guaranteed.

3.5.3.1 Tensile. Give the 0.2% proof strength, or yield strength, for a 0.2% offset and the ultimate strength. Give percent elongation in the longitudinal (rolling or extruding) direction with a 50 mm (1.97 in) gauge length. Testing should be in accordance with ISO/R82, R86, and R375; EN 10002 PT 5*; ASTM E8; BS 18.

3.5.3.2 Compression. Give the 0.2% proof strength, or yield strength, and the ultimate strength. Testing should be in accordance with ASTM E9.

3.5.3.3 Bearing. Give the 2% offset bearing strength. Testing for pin bearing should be in accordance with ASTM E238.

3.5.3.4 Shear. Give the shear strength. Testing should be in accordance with ASTM B565.

3.5.4 Fatigue Properties. Desirably give minimum stress/number of cycles (S/N) curves between 103 and 106 cycles with a (mean - 2 x standard deviation) probability of survival on a log-normal distribution for stress ratios 0, +0.5, -1 for the following specimens as required:

Smooth-base material

Notched-base material

Butt welds

Fillet welds

Connections other than welds

3.5.5 Fracture Data. Compare with other alloys and give the parameters KC and KIC with details of the test specimen. Testing for KIC should be to ASTM E399. Threshold stress intensity Kth and crack propagation data based on the fracture mechanics should be available for base material and welds/HAZ’s.

3.5.6 Corrosion Resistance. Briefly compare corrosion resistance with that of other alloys of the same material. Special corrosion characteristics including the effects of heat treatment, welding, and aging should be mentioned if they differ greatly from similar alloys.

3.5.7 Stress Corrosion. Briefly compare with other similar alloys. Give the threshold stress below which stress-corrosion cracks do not initiate for smooth specimens, preferably in four-point bending, stating the time, environment, material, grain structure, and specimen orientation.

3.5.8 Heat Treatment. Give details of any heat-treatment processes pertaining to the material. Appendix D - International Temper Equivalents for Aluminum ALLOYS summarizes heat treatment equivalents for the three member countries.

3.5.9 Welding and Joining. Give recommended welding electrodes and any special joint-preparation requirements.

3.5.10 Brittle Fracture. It should be shown that the material, as used in the structure, will not be subject to brittle fracture at the required low temperature by quoting nationally accepted tests or the transition temperature if applicable.

3.6 Data Required for Selected Composites.

3.6.1 General. This section includes glass, aramid, and carbon composites. It considers only the properties of the most commonly used cured composite for preferred methods of manufacture and adhesives. Individual properties of fibers and resin matrix should be entered on the Data Sheet shown in Appendix E - COMPOSITE MATERIALS DATA FORM, if available. Although these properties determine composite characteristics, they are no more than a guide to the expected composite material property levels. Physical and mechanical property data should be measured at 23 ± 2 °C (73 ± 4 °F) and 50 ± 5% relative humidity (RH). Mechanical property data should also be measured at temperature and humidity conditions representative of severe operation, 50 ± 2 °C (122 ± 4 °F) and 85 ± 5% RH, or a higher or lower* condition, if specified. Preconditioning is required to achieve the equilibrium humidity content and temperature consistent with the test temperature and moisture (see ASTM D618 on preconditioning).

3.6.2 Composite Description. Sufficient detail should be specified to define the composite constituents uniquely either in terms of manufacturers' coding or to accepted specifications. Layup geometry, number of plies, volume fraction, and final thickness of the composite should be given.

3.6.3 Processing.

The method of producing the cured composite form should be stated with details of curing times, pressures, and temperature cycles.

3.6.4 Physical Properties.

3.6.4.1 The density, fiber volume fraction, and void content should be stated and determined in accordance with appropriate published standards. Calibrated alternative methods are accepted.

3.6.4.2 Thermal expansion coefficient related to the operating temperature range should be given.

3.6.4.3 Equilibrium moisture content and relative linear dimensional changes should be determined for the most severe operating conditions (temperature and humidity). This information should be used to specify preconditioning for test specimens. The glass transition temperature for the composite should also be given.

3.6.5 Basic Lamina Mechanical Properties.

3.6.5.1 The level of mechanical properties depends upon the strain rate and the physical state of the material in respect to temperature and moisture content. Properties for design should include measurement at the minimum median and maximum operating temperatures and show changes associated with moisture pick up. Preconditioning test conditions should be as specified in paragraph 3.6.1. Property data should be provided for individual lamina and for the (laminated) composite. The required lamina properties are identified in Appendix E - COMPOSITE MATERIALS DATA FORM, and include tensile and compressive strength parallel and orthogonal to the fiber direction and inplane shear strength (see ASTM D3039, D3410, and D3518). Minimum guaranteed fiber strain must also be reported. Interlaminar shear strength (or transverse shear strengths for other than laminated composites) should be measured by a procedure to be agreed upon.

3.6.5.2 In addition, longitudinal, transverse, and shear moduli and Poisson's ratios should be obtained for the individual lamina. Longitudinal tensile, compression, flexural strength and Poisson's ratios should be obtained on full thickness (laminated) composite coupons with the stacking sequence to be utilized in production at severe operating conditions only as specified in paragraph 3.6.1. Geometric discontinuities should be considered.

3.6.5.3 The mean value and standard deviation of each property should be determined from a minimum sample size of 6.

3.6.5.4 Application of any failure criteria to establish a composite strength analysis for a multiaxial laminate in either a uniaxial or multiaxial stress state requires a coherent set of basic ply properties as given in Appendix E - COMPOSITE MATERIALS DATA FORM. Test methods to be based on appropriate published standards.

3.6.6 Fatigue Properties.

3.6.6.1 Fatigue properties should be determined by test on appropriate specimens (ASTM D3039 provides specimen information). Test conditions should be designed to avoid heat build-up (ASTM D3479).

3.6.6.2 A testing program can be performed which provides minimum S/N curves between 103 and 106 cycles with a 97.5% probability of survival on a log normal distribution for stress ratios of 0, +0.5, -1.

3.6.6.3 Alternatively, testing can be performed for the most severe operational stress envelope, i.e. between the minimum and maximum transient stress to which the component may be subjected, increased for a number of cycles equal to 1.8 times the design life.

3.6.6.4 In either case, tests should be performed on full thickness specimens with the design stacking sequence for both smooth specimens and specimens containing geometric discontinuities (holes and/or notches) representative of design items.

3.6.6.5 Correctly loaded components should be tested.

3.6.7 Impact Susceptibility. Determine threshold of impact induced interlaminar damage by drop weight tests; specification to be agreed upon.

3.6.8 Stress Rupture/Creep.

Determine to agreed specifications constant stress versus time curves for selected critical material stress cases. Creep behavior should be investigated at the maximum service temperature. The tensile specimen (ASTM D3039) is appropriate for both creep and stress rupture testing.

3.7 Data Required for Selected Adhesives.

3.7.1 General. This section relates to adhesives for structural composite bonded joints and metal attachments. The performance of adhesives can be significantly influenced by the prior preparation of the surfaces bonded. Guaranteed minimum strength properties must be established by testing representative joints. Typical data requirements are indicated in Appendix F - ADHESIVE DATA FORM. Test conditions (temperature and humidity) and preconditioning should be as specified in paragraph 3.6.1 for composites. Correctly loaded joints should be tested.

3.7.2 Adhesive System Description. Described by giving the manufacturer's coding and supplier and the form of adhesive used (liquid, paste, or film). The nature of the adhesive should be stated giving intended application (adherends and service environments). The system components should be listed including compatible primer systems.

3.7.3 Processing Requirements. Indicate surface preparation, assembly methods, and pressures and time/temperature cycles to obtain stated properties. Minimum curing temperatures should be given and range of allowable bond line thickness stated.

3.7.4 Physical Properties of Cured Adhesive.

State the glass transition temperature.

State the transverse electrical resistivity.

3.7.5 Mechanical Properties. The level of mechanical properties may be affected by the strain rate of testing and the physical condition of the bonded system. Mechanical property data should be developed at the conditions defined in paragraph 3.6.1. The following data should be reported: tensile and shear load, and peel strength; tensile and shear moduli, elastic, and inelastic tensile and shear strain limits. Application of the data in Appendix F - ADHESIVE DATA FORM, to selected joint configurations should take into account stress concentrations arising from geometrical factors and adherend stiffness. Test methods should be in accordance with appropriate published standards, such as ASTM E229 (shear strength and modulus), ASTM D897 (tensile strength), ASTM D1876 or D3167 (peel strength).

3.7.6 Fatigue Properties. Fatigue properties of many adhesives are particularly sensitive to cycling rate and should be determined under conditions close to that of use under the most severe operating environment. The following fatigue tests should be performed: tension, shear, and peel. Either minimum S/N to failure curves should be developed or fatigue tests specific to the design load envelope should be carried out as specified in paragraph 3.6.6. Adhesive fatigue properties may be compared using standard test methods but allowance for geometrical stress concentrations should be made on other joint geometries and testing of representative test coupons is essential.

3.7.7 Environmental Degradation. A ranking of the expected durability of selected adhesive/adherend surfaces should be given in terms of wedge test crack propagation or stressed lap shear test, but specific factors can be obtained only by testing representative joint details. Full details of surface preparation techniques should be given. The rate of environmental degradation will also depend on the specific geometry and stress system applied to the bonded joint.

3.7.8 Creep Behavior. To be based on ASTM D2294 or British Standards 3250 Part C7 with preference for a thick adherend single-lap shear specimen. Creep behavior should be investigated at the maximum service temperature.

IV. DESIGN PARAMETERSPRIVATE

4.1 General. The design parameters below are to be used unless modified by the equipment requirement/specification. Generally, the parameters represent the worst conditions achieved during normal service, and average usage should not be so severe. In some instances a desirable alternative parameter is given, and it should be regarded as an improvement that the designer should try to achieve. The designer will have to balance cost and effect with the achievement of desirable parameters, and it may not be possible to achieve all parameters. Abnormal service parameters should be covered by special tests on the equipment. Parameters are given for clear span bridges, piers, floating bridges, and rafts.

4.2 Clear-Span Bridge and General Parameters.

4.2.1 Minimum Clear Roadway Width (STANAG 2021 edition 6):

4-12

13-30

31-70

71-100

Above 100

2.75 m (9 ft)

3.35 m (11 ft)

4.00 m (13 ft, 2 in)

4.50 m (14 ft, 9 in)

5.00 m (16 ft, 5 in)

5.50 m (18 ft)

5.50 m (18 ft)

7.30 m (24 ft)

8.20 m (27 ft)

Not allowed

4.2.2 Truss Bridge Roadway Width. For through truss bridges with exterior curbs: Face of curb to inside of truss to be 250 mm (10 in) minimum from 300 mm (12 in) above the deck to the top of the truss.

4.2.3 Footwalk Width. Width will be a minimum of 650 mm (2 ft, 2 in).

4.2.4 Trackway width for MLC 31 and above. Minimum width for single trackway will be 1,525 mm (5 ft). Maximum center gap will be 950 mm (3 ft, 1 in). (Dimensions must be checked to suit all vehicles expected to use the trackway.)

4.2.5 Bank Conditions.

4.2.5.1 For Assault {Close Support} bridges, the height difference, h, between home and far banks is essentially 1 in 10 (10%) and desirably 1 in 5 (20%) multiplied by the length of the span up to a maximum of 6.0 m (19 ft, 8 in). For Assault {Close Support} bridging, h, is measured from the home bank slope projection.

4.2.5.2 For Support {General Support} bridges, the maximum height difference, h, between home and far banks is essentially 1 in 10 (10%) multiplied by the length of the span up to a maximum of 3.0 m (9 ft, 10 in). For Support {General Support} bridges, h, is measured from the home bank horizontal projection.

4.2.5.3 For safety purposes to prevent wheeled vehicles slipping sideways off the bridge, transverse deck slopes between any two points on the bridge deck surface under live load shall not exceed 1 in 10 (10%). This is known as the serviceability limit. In the case of twin trackway bridges with structural infill decking, this is considered part of the bridge deck surface.

4.2.5.4 Consistent with the serviceability limit, it must be possible for bridges and the launching system to accept uniform transverse slopes*, or steps, bumps or depressions equivalent to a transverse slope, anywhere on the bankseat supports of the following gradients:

Assault {Close Support} Bridges (CSBs)

5.0% (1 in 20)

Support {General Support} Bridges (GSBs)

2.0% (1 in 50)

Line of Communication (LOC) Bridges

0.5% (1 in 200)

*Note: It must also be considered that near and far banks can have like or opposing transverse slopes, i.e., +1 in 20 near bank, ±1 in 20 far bank.

4.2.5.5 For multi-span bridges (including combination bridges and bridges supported on a fixed or floating pier), the same conditions for transverse slopes or irregularities must be considered to be applicable at the intermediate supports. For continuous floating bridges (e.g. Ribbon or M3) the same transverse bankseat criteria shall apply to the supporting ramps providing access and egress to the roadway.

4.2.6 Bank Bearing Pressure.

4.2.6.1 Assault {Close Support} bridges shall be designed to bear uniformly on a projected length of 0.75m (2 ft, 6 in) measured from the extreme ramp toe. Under such conditions maximum bearing pressures should not exceed 380 kN/m2 (4.0 tons/ft2) under any live load up to and including MLC70 (T and W), including an allowance of 1.2V, dead load and the most significant secondary load. In extreme conditions, allowing for bridge movement, ramp bearing length can reduce to 0.25m (10 in) before reinstatement, but corresponding pressures shall not exceed 1,140 kN/m2 (11.9 tons/ft2) under the same load.

4.2.6.2 Support {General Support} bridges shall be designed to bear uniformly on a projected length of 1.0m measured from the effective end of bridge (which might exclude approach ramps). Under such conditions maximum bearing pressures should not exceed 425 kN/m2 (4.4 tons/ft2) under any live load up to and including MLC70 (T and W), allowing for the dynamic effects of multiple vehicles, dead load and the most significant secondary load. In extreme conditions, allowing for bridge movement, effective bearing length can reduce to 0.5m (1 ft, 8 in) before reinstatement, but corresponding pressures shall not exceed 850 kN/m2 (8.9 tons/ft2) under the same load.

4.2.6.3 In special circumstances involving combination (overlapping) bridging or overbridging, extreme bearing pressures shall not exceed 40,000 kN/m2 (5,800 psi) and the effects of local crushing must be considered at the interface between structures. The same consideration of local damage must be given to bearing on hard, high spots when bridges are supported on the nominal full bearing area as defined above.

4.2.7 Depth of Bridge at Ramp Toe:

Maximum

Desirable 100 mm

50 mm or less 75 mm

Minimum possible

4.2.8 Bridge Deck Slopes.

The allowable longitudinal slopes for a bridge with level supports and no applied loads, Ai, are given in the following table. The transverse slope allowing for the support conditions of paragraph 4.2.5 and the unfactored fully eccentric vehicle load, V, with impact should not exceed 1 in 10.

Short ramp or sloping end of bridge up to 3 m (9 ft 10 in) long:

Ramp or sloping end of bridge longer than 3 m (9 ft 10 in):

Change of slope on bridge other than at sloping ends:

1 in 5

1 in 7 or less

1 in 6

1 in 10 or less

1 in 6

1 in 10 or less 1 in 7

1 in 10 or less

1 in 9

1 in 14 or less

1 in 10

1 in 20 or less

4.2.9 Wind Velocity and Pressure. The wind velocities and pressures are the maximum values to which the bridge should be designed:

During construction /launching

On bridge and crossing vehicle

On bridge alone

29.2

38.8

58.3 0.138

0.245

0.552 2.88

5.11

11.51

4.2.10 Vehicle Design Crossing Speed. Essential speeds are the maximum speeds under normal field conditions and the speeds up to which bridges must be tested:

Essential

Desirable 25 km/h (15 mi/h)

40 km/h (25 mi/h) 15 km/h (9 mi/h)

25 km/h (15 mi/h)

4.2.11 Impact. Vehicle induced loads will be increased by the following factors to cover crossing speeds up to 25 km/h (15 mi/h):

Impact Factors

and Deflection Shear Force

Interior

Ramp 1.15

1.2

1.2

It should be noted that these values cover modern suspension vehicles for the desirable velocity and old suspension and high pitch inertia vehicles for the essential velocity according to paragraph 4.2.10. The given factors are typical values so that for extreme cases a more detailed investigation for design is recommended. An increase of 15% for impact will be added to the bridge dead load, D, and launching equipment if appropriate during launching.

The maximum included static load multiplied by the impact factor results in the maximum induced dynamic load.

4.2.12 Mud Load (M). The following load will be used when calculating the effects of mud on the roadway surface: 0.75 kN/m2 (15.67 lbf/ft2).

4.2.13 Snow and Ice Load (S). The following load will be used if it has a greater effect than the mud load, M (300 mm (12 in) of loose snow of areal density): 0.37 kN/m2 (7.7 lbf/ft2).

4.2.14 Footwalk Loading (F). Footwalks are those structures which are attached to existing structures e.g. as add-on kits or stand alone structures. Footwalks are intended primarily for the support of crossing troops and secondarily in support of local pedestrian traffic for local commerce. Loadings will include the fully outfitted combat soldier and/or could additionally include bicycles, motorcycles, all terrain vehicles, livestock and horses. The value of the design loading to be considered on the footwalk could be adjusted depending on the intended use of the structure and the ability to restrict types of traffic.

4.2.14.1 The main members of the footwalk shall be designed for a maximum live loading of 4.0 kN/m2 (83.56 lbf/ft2) for spans up to 30 m (98 ft, 5 in). The load will then be reduced linearly to 3.0 kN/m2 (62.67 lbf/ft2) for spans up to 60 m (196 ft, 10 in). For spans beyond 60 m (196 ft, 10 in), the load will remain constant. Main members shall be defined as those members, which comprise the main structural elements of the footwalk, e.g., girders, trusses, arches etc.

4.2.14.2 The secondary members shall be designed for a maximum live load of 4.0 kN/m2 at all spans. Secondary members shall include decks, supporting floor systems, secondary stringers, floorbeams and connections to the main members.

4.2.14.3 The force to be considered for a laden soldier will be 1.27 kN (286.65 lbf), which is the combination of the weight of the individual soldier at 0.88 kN (198.45 lbf) and the weight of his backpack at 0.39 kN (88.2 lbf).

4.3 Combination Bridging.

4.3.1 Combination bridging may be used in wet or dry gaps where the clear span to be bridged exceeds the span capability of a single bridge system. In wet gaps, the use of combination bridging into water shall be permissible under the following conditions:

Maximum surface water speed at mid-stream not to exceed 1.5 m/s (2.9 knots).

Under bridge dead load alone, water level shall not to be within 100mm (4 in) of any trafficable deck surface.

Combination bridges must not be launched unless there is some non-metallic interface between the bridges to spread the anticipated live load and prevent slipping in a wet environment under live vehicle trafficking.

4.3.2 The longitudinal slope of any span deployed in a combination must not exceed the capability of a simply supported single span under the same load condition. The longitudinal slope is defined as the slope of an imaginary line joining the home and far bank toe pins of a single span bridge.

4.3.3 For the purpose of designing combination bridges, the launch plane of the launch vehicle is defined as the nominal extension of the surface on which the launch vehicle tracks or wheels are located.

4.3.4 Under dead load conditions, acute angles between the underside bottom chord of a subsequent span, and the deck of the underlying span are to be greater than 3 degrees to allow for subsequent deflection under live load, and avoid the possibility of knife-edge loading.

4.3.5 Ingress and egress should allow vehicles a straight run on and off the bridge to minimize the need for slewing.

4.3.6 The launching of the first bridge of a combination bridge is restricted to a transverse slope of 1 in 20 (5%). If opposing bankseat cross slopes result in a combined angular deviation of more than 1 in 20 (under dead load), instability could result at bridge intersections.

4.3.7 Conditions of the bed of the river or gap must be determined if the combination bridge is to be laid with minimal risk. If any doubt exists as to the condition of the bed, a survey involving divers must be undertaken. The bed should be free from obstructions and firm enough to support the bridge toes.

4.3.8 The depth of any silt or soft material must be known, and some assessment made of likely sinkage. Whilst a uniform bed is desirable, it must be accepted that live load trafficking or scouring from hydrodynamic forces can produce settlement. The limiting cross slope and irregularities for bridges used in combination shall be no worse than the limiting support conditions prevailing for simply supported single spans.

4.3.9 The toes of a second or third span in a combination might be restricted to specific locations along the length of the first bridge. This might be necessary to avoid structural overloading of the first span in shear near the ramps, or in bending as a result of the additional dead load of subsequent bridges.

4.3.10 The maximum lateral misalignment permitted between bridges shall be no more than 75mm.

4.3.11 For second and subsequent spans, due account must be taken of possible bridge movement as a result of vehicle crossings, particularly if bridges are on a downward longitudinal slope, the junction between bridges is wet or under water, or likely to be subjected to significant (>50) crossings.

4.3.12 In order to minimize the need to reinstate combination bridges due to bridge movement, it is advised that where the overall bridge length allows, the toe is positioned up to 2m (6 ft, 7 in) back from the limiting toe position, measured in the direction opposite to that trafficking. Alternatively, there should be some system for the anchorage of bridges from under armor, or the remote attachment of one bridge to another to prevent slippage occurring.

4.3.13 The amount of bridge movement is dependent on various factors and conditions such as mass of the vehicle, type of vehicle, clear span of the bridge, degree of longitudinal bridge slope, ground bearing capacity and friction conditions at the supports. Generally, the heavier the vehicle and the greater the clear span, more bridge movement is to be expected. Bridges must be reinstated if the anticipated throughput of traffic results in sufficient movement to reduce bearing areas to minimum safe limits. The minimum safe bankseat bearing length for Close Support Bridges (CSBs) shall be taken as 0.25m (10 in).

4.4 Piers.

4.4.1 Dimensions.

4.4.1.1 In the absence of a User requirement, the following dimensions are recommended for the design of piers and trestles which might be installed in wet gaps:

Gap Depth:

Essential

Water Depth:

Essential

4 m (13 ft, 1 in)

5 m (16 ft, 5 in)

3 m (9 ft, 10 in)

4 m (13 ft, 1 in) 7 m (23 ft)

12 m (39 ft, 4 in)

6 m (19 ft, 8 in)

6 m (19 ft, 8 in)

4.4.1.2 In addition, there is to be a minimum clearance of 100mm (4 in) between any point on the trafficable deck surface and the surface of the water, when the total bridge system is deployed without live load.

4.4.1.3 In the case of combination bridges on piers or trestles, due consideration must be given to the obtuse angle (() between bridge deck surfaces (which could affect trafficability), the acute angle (() between the deck of a first span and the undeflected bottom chord of a subsequent span (which could produce ‘knife–edge’ loading), and the relative overlap (() between bridges (which could be reduced with trafficking as a result of bridge movement). See Figure 4-1.

4.4.1.4 Minimum suggested values for these parameters are:

( = 149.0 degrees, ( = 3.0 degrees, ( = 0.75 m (2 ft, 6 in)

4.4.2 Grillage Bearing Pressure.

Maximum: 160 kN/m2 (1.7 ton/ft2). Sinkage is acceptable consistent with stability and recovery.

4.4.3 Current Speeds. The current speeds for piers are the same as those given for floating bridges and rafts (paragraphs 4.5.1).

4.4.4 Pier Support. These should articulate in any direction to allow a longitudinal and transverse bridge slope of at least ±1 in 10 (±10%) under live vehicle loading.

4.5 Floating Bridges and Rafts.

4.5.1 Bridging Current Speeds:

Construction and normal use:

Unladen equipment survival:

Minimum:

Desirable:

2.5 m/s (4.9 knots)

3.5 m/s (6.8 knots)

5.0 m/s (9.7 knots)

4.5.2 Raft Speed Laden:

Minimum:

Desirable:

2.5 m/s (4.9 knots)

3.5 m/s (6.8 knots)

4.5.3 Worst Case Shallow Water, Fast Current Condition: Midstream: 2 m (6 ft, 7 in) of water running at 2.5 m/s (4.9 knots).

4.5.4 Worst Case Shallow Water Condition at Bank for Ramp and Flotation: River bed slopes down 1 in 7 from water's edge.

4.5.5 Bank-Height/Ramp-Elevation Ranges:

Upward:

Minimum

Downward:

+1.5 m (4 ft, 11 in)

+2.0 m (6 ft, 7 in)

(Relative to water level.)

Bottom of ramp toe should be level with bottom of main floating structure.

The ramp slopes on rafts and bridges should not exceed the values given in paragraph 4.2.8 for the worst condition of loading.

If these bank heights are used for launching floating equipment, it is not realistic to combine them with the worst case shallow water depth in paragraph 4.5.4. A water depth of 2.0 m (6 ft, 7 in) can be assumed 8.0 m (26 ft, 3 in) from the water’s edge.

4.5.6 Pontoon Bottom-Skin Load. The pontoon bottom-skin load should not exceed 96 kN/m2 (2,005 lbf/ft2).

4.5.7 Minimum Freeboard. The following minimum freeboard values with the maximum MLC vehicle load(s) fully eccentric are considered adequate for normal equipment configurations at the design current speed. See paragraph 4.5.1.

Minimum Freeboard of Pontoon

Pneumatic Floats

Rigid Open Pontoons

Rigid Closed Pontoons

Rigid, Continuous Closed Pontoons

(4)

(9)

(6)

(2)

(0)

(5)

(4)

(0)

4.5.8 Trim. A floating bridge or raft with a vehicle at permitted eccentricity should not trim so that the deck slope is more than 1 in 20 under the worst permitted hydrodynamic conditions.

4.6 Typical Vehicle Data for Design.

Height of

Center of Gravity (CG)

Center of Pressure

1.02 1.05 1.07 1.09 1.12 1.14

1.18

1.24

1.30

1.36

1.42

1.48

1.54

1.60

1.72

1.90 (40.2)

(41.3)

(42.1)

(42.9)

(44.1) (44.9)

(46.5)

(48.8)

(51.2)

(53.5)

(55.9)

(58.3)

(60.6)

(63.0)

(67.7)

(74.8) 7.32 8.23

9.13

10.04

10.94

11.85

13.33

15.47

17.74

20.00

22.26

24.53

26.79

29.06

33.59

40.45 (78.8) (88.6)

(98.3)

(108.1)

(117.8)

(127.6)

(143.5)

(166.5)

(191.0)

(215.3)

(239.6)

(264.0)

(288.4)

(312.8)

(361.6)

(435.4) 1.18 1.20 1.23

1.25

1.28

1.30

1.34

1.40

1.47

1.53

1.59

1.65

1.72

1.78

1.90

2.09 (46.5) (47.2)

(48.4)

(49.2)

(50.4)

(51.2)

(52.8)

(55.1)

(57.9)

(60.2)

(62.6)

(65.0)

(67.7)

(70.1)

(74.8)

(82.3)

2.40 2.40

2.40

2.40

2.40

2.40

2.40

2.40

2.40

2.40

2.20 2.00

2.00

2.00

2.00

2.00 (94.5)

(94.5)

(94.5)

(94.5)

(94.5)

(94.5)

(94.5)

(94.5)

(94.5)

(94.5)

(86.6)

(78.7)

(78.7)

(78.7)

(78.7)

(78.7) 6.12 12.24 20.24

24.17 32.66

38.10

45.00

45.00

45.00

45.00

45.00

45.00

45.00

45.00

45.00

45.00 (65.9) (131.8)

(217.9)

(260.2)

(351.5)

(410.1)

(484.4)

(484.4)

(484.4)

(484.4)

(484.4)

(484.4)

(484.4)

(484.4)

(484.4)

(484.4) 2.20 2.20

2.20

2.20

2.20

2.20

2.20

2.20

2.20

2.20

2.20

2.20

2.20

2.20

2.20

2.20 (86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

(86.6)

4.7 Temperature and Environment. The environmental effects due to the required categories must be considered(. Thermal stresses and long-term degradation due to temperature and humidity must be considered.

V. LOADS AND LOAD COMBINATIONSPRIVATE

5.1 General. The designer will use the most critical loading obtained from paragraph 5.3, Military Bridge Loads, using the values given here or detailed in Section IV, DESIGN PARAMETERS and the combinations given in paragraph 5.4, Load Combinations. The worst support conditions must also be taken into account.

5.2 Deflections. Deflections are not limited directly by this code but must be considered when they cause changes in loading, affect fit or alignment, or affect the use of equipment.

5.3 Military Bridge Loads.

5.3.1 Dead Load (D). The structure dead load, D, shall consist of the weight of the complete bridge for the structure in place or of the appropriate bridge components.

5.3.2 Vehicle Load (V).

5.3.2.1 The vehicle load, V, is represented by the hypothetical vehicle of the required load class depicted in STANAG 2021 (see Appendix C - CHARACTERISTICS OF HYPOTHETICAL VEHICLES USED FOR THE RATING OF THE MLC OF VEHICLES AND BRIDGES). The most critical loads induced by any of the following with the impact factor will be used:

The hypothetical tracked vehicle.

The hypothetical wheeled vehicle.

The hypothetical axle load.

The hypothetical single-wheeled loads.

If a vehicle other than the hypothetical STANAG vehicle is used, problems will be encountered with variations in load class or the load to give the correct bending moment or shear. These occur due to changes in bridge length and vehicle width.

5.3.2.2 For tracked vehicles, the load will be applied as follows for each track: For Military Load Class (MLC) 30 and above, there will be 6 contact areas and for MLCs lower than 30 there will be 5 contact areas. These represent the road wheels and must be fitted into the hypothetical track length allowing for the contact area length. The width of each contact area is taken as the hypothetical vehicle track width and the contact area length along the track is taken so that the working load bearing pressure:

If the number of contact areas is reduced or increased, pb must be changed accordingly. For wheeled vehicles, the wheel load will be applied on a contact area, with the nominal tire width and load of the hypothetical vehicle (Appendix C – CHARACTERISTICS OF HYPOTHETICAL VEHICLES USED FOR THE RATING OF THE MLC OF VEHICLES AND BRIDGES) which will produce a contact pressure of 1.25 times the tire pressure at working load not to exceed 1100 kN/m2 (11.2 kp/cm2, 160 lbf/in2).

5.3.2.3 Consideration should be given to changes in individual wheel and tank-track bogie loads as vehicles pitch or negotiate changes in slope.

5.3.3 Mud Load (M). The mud load, M, in the design parameters will be considered over the roadway area. Reductions in loading may be made for proven self-cleaning decks. Accumulations of mud on vehicles will not be considered. It is assumed that mud is removed from bridges before they are recovered or retrieved. If this is not possible, a percentage of the mud load, M, should be included in the weights for retrieval purposes. This percentage is a function of the particular bridge design and will range from 10 to 25% of the total. The impact factor should be considered in addition.

5.3.4 Snow and Ice Load (S). The snow and ice load, S, in the design parameters is applied…