Attachment_8_Unified_Facilities_Criteria.pdf

UFC 3-320-06A

1 March 2005

UNIFIED FACILITIES CRITERIA (UFC)

CONCRETE FLOOR SLABS ON

GRADE SUBJECTED TO HEAVY

LOADS

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

FA4803-17-Q-A013

Attachment 8

UNIFIED FACILITIES CRITERIA (UFC)

CONCRETE FLOOR SLABS ON GRADE SUBJECTED TO HEAVY LOADS

Any copyrighted material included in this UFC is identified at its point of use.

Use of the copyrighted material apart from this UFC must have the permission of the copyright holder.

U.S. ARMY CORPS OF ENGINEERS (Preparing Activity)

NAVAL FACILITIES ENGINEERING COMMAND

AIR FORCE CIVIL ENGINEER SUPPORT AGENCY

Record of Changes (changes are indicated by \1\ ... /1/)

Change No. Date Location

This UFC supersedes TM 5-809-12, dated 25 August 1987. The format of this UFC does not conform to UFC 1-300-01; however, the format will be adjusted to conform at the next revision.

The body of this UFC is the previous TM 5-809-12, dated 25 August 1987.

FOREWORD

\1\ The Unified Facilities Criteria (UFC) system is prescribed by MIL-STD 3007 and provides planning, design, construction, sustainment, restoration, and modernization criteria, and applies to the Military Departments, the Defense Agencies, and the DoD Field Activities in accordance with USD(AT&L) Memorandum dated 29 May 2002. UFC will be used for all DoD projects and work for other customers where appropriate. All construction outside of the United States is also governed by Status of forces Agreements (SOFA), Host Nation Funded Construction Agreements (HNFA), and in some instances, Bilateral Infrastructure Agreements (BIA.)

Therefore, the acquisition team must ensure compliance with the more stringent of the UFC, the SOFA, the HNFA, and the BIA, as applicable.

UFC are living documents and will be periodically reviewed, updated, and made available to users as part of the Services’ responsibility for providing technical criteria for military construction. Headquarters, U.S. Army Corps of Engineers (HQUSACE), Naval Facilities Engineering Command (NAVFAC), and Air Force Civil Engineer Support Agency (AFCESA) are responsible for administration of the UFC system. Defense agencies should contact the preparing service for document interpretation and improvements. Technical content of UFC is the responsibility of the cognizant DoD working group. Recommended changes with supporting rationale should be sent to the respective service proponent office by the following electronic form: Criteria Change Request (CCR). The form is also accessible from the Internet sites listed below.

UFC are effective upon issuance and are distributed only in electronic media from the following source:

• Whole Building Design Guide web site http://dod.wbdg.org/.

Hard copies of UFC printed from electronic media should be checked against the current electronic version prior to use to ensure that they are current.

AUTHORIZED BY:

DONALD L. BASHAM, P.E.

Chief, Engineering and Construction U.S. Army Corps of Engineers

DR. JAMES W WRIGHT, P.E.

Chief Engineer Naval Facilities Engineering Command

KATHLEEN I. FERGUSON, P.E.

The Deputy Civil Engineer DCS/Installations & Logistics Department of the Air Force

Dr. GET W. MOY, P.E.

Director, Installations Requirements and Management Office of the Deputy Under Secretary of Defense (Installations and Environment) http://www.wbdg.org/pdfs/ufc_implementation.pdf https://65.204.17.188/projnet/cms/version2/index.cfm?WORKFLOW=CMS_CCRQAdd&Action=IDFORM&SecureTry=1 http://dod.wbdg.org/

ARMY TM 5-809-12

AIR FORCE AFM 88-3, Chap. 15

DEPARTMENTS OF THE ARMY AND

THE AIR FORCE TECHNICAL MANUAL

CONCRETE FLOOR SLABS

ON GRADE SUBJECTED

TO HEAVY LOADS

DEPARTMENTS OF THE ARMY, AND THE AIR FORCE

AUGUST 1987

*TM 5-809-1/AFM 88-3, Chap. 15 i

TECHNICAL MANUAL HEADQUARTERS

NO.5-809-12 DEPARTMENTS OF THE ARMY

AIR FORCE MANUAL AND THE AIR FORCE

NO. 88-3, CHAPTER 15 WASHINGTON, D.C., 25 August 1987

CONCRETE FLOOR SLABS ON GRADE SUBJECTED TO HEAVY LOADS

CHAPTER 1. INTRODUCTION

Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1- Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 1- Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Basic considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

CHAPTER 2. BASIS OF FLOOR SLAB ON GRADE DESIGN

Stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 Vehicle-imposed loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 Stationary live loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 Wall loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

CHAPTER 3. DETERMINATION OF FLOOR SLAB

REQUIREMENTS

Vehicular loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3- Traffic distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3- Stationary live loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 Wall loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4 Unusual loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

CHAPTER 4. SITE INVESTIGATION

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4- Subgrade conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 Envirormental conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 Concrete strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4 4-

CHAPTER 5. DESIGN PROCEDURE

General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5- Floor slab loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 Subgrade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 Base courses Reinforced Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 Steel reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 Joint types and usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 Floor slab geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8 Fiber reinforced design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

* This manual supersedes TM 5-809-12/AFM 88-3, Chapter 15, dated 1 April 1977.

TM 5-809-12/AFM 88-3, Chap. 15 ii

Page APPENDIX A. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

APPENDIX B. EQUATIONS FOR COMPUTING THE ALLOWABLE

WALL LOADS NEAR CENTER OF SLAB OR NEAR

KEYED OR DOWELED JOINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

APPENDIX C. DESIGN EXAMPLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1 BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . BIBLIO-1

LIST OF FIGURES

Figure 3-1 Widths of thickened slabs and slab edge conditions under wall loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-

5-1 Design curves for concrete floor slabs by design index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-

5-2 Design curves for concrete floor slabs for heavy forklifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-

5-3 Reinforcement for odd-shaped slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-4 Design thickness for reinforced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-floor slabs 5-5 Typical floor slab joint layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-6 Contraction joints for reinforced and nonreinforced floor slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-7 Joint sealant details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-8 Contraction joint details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-9 Doweled construction joints for concrete floor slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-10 Keyed construction joints for concete floor slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-11 Doorway slab design for vehicular traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-12 Isolation joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-13 Thickened-edge joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-14 Joints in concrete floor slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-15 Design curves for fiber-reinforced concrete floor slab by design index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-16 Design curves for fiber-reinforced concrete floor slab for heavy forklifts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-17 Deflection curves for fiber-reinforced concrete floor slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-18 Allowable deflection for jointed fiber-reinforced concrete floor slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-

LIST OF TABLES

Table 3-1 Maximum allowable stationary live load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-

3-2 Minimum thickness of thickened floor slab for wall load near center of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-slab or near keyed or doweled joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-

3-3 Maximum allowable wall load near free edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-

4-1 Typical values of modulus of subgrade reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-

5-1 Traffic categories for design index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-2 Recommended spacing of transverse contraction joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5- 5-3 Dowel size and spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-

TM 5-809-1/AFM 88-3, Chap. 15

1-1

CHAPTER 1

INTRODUCTION

1-1. Purpose. g. Vibratory loads. Dynamic and/or oscillatory This manual prescribes the criteria for the design of concrete floor slabs on grade in buildings for heavy loads and is applicable to all elements responsible for military construction. Heavy loads in buildings such as warehouses include moving loads, stationary live loads, and wall loads.

1-2. Scope.

Theoretical concepts, practical applications, basis of design, and design procedures for heavy loads are discussed in this manual. Related criteria for light-loaded areas such as office spaces are separately treated in TM 5-809-2/AFM 88-3, Chap. 2. Criteria for areas subjected to vibratory loadings are included in TM 5-81 8-1/AFM 88-7, Chap. 1. For design criteria outside the scope of this manual, industry standards are recommended.

1-3. Definitions.

The following definitions have been adopted for the manual:

a. Slab on grade. Concrete slab supported di-rectly on foundation soil.

b. Light loads. Loads which consist of (compa-rable) forklift axle load of 5 kips or less and stationary live loads less than 400 pounds per square foot.

c. Heavy loads. Loads which consist of any one of the following: moving live loads exceeding a forklift axle load of 5 kips, stationary live loads exceeding 400 pounds per square foot, and concentrated wall loads exceeding 600 pounds per linear foot.

d. Wall load. Concentrated loads imposed by walls or partitions.

e. Dead load. All the materials composing the permanent structure, including permanent wall loads and all equipment that is fixed in position.

f. Live load. Loads imposed by the use and occupancy of the structure.

(1) Moving live load. Loads imposed by ve-hicular traffic such as forklift trucks.

(2) Stationary live load. Loads imposed by movable items such as stored materials.

loading of significant magnitude.

h. Design load. The effects of stationary live, dead, and wall loads and moving live loads. Dead loads of floor slabs on grade are ignored.

i. Special soils. Soils which exhibit undesirable properties for construction uses such as high com-pressibility or swell potential.

j. Nonreinforced slab. Concrete slab resting on grade containing minimal distributed steel, usually of welded wire fabric (WWF), for the purpose of limiting crack width due to shrinkage and tempera-ture change.

k. Reinforced slab. Concrete slab resting on grade containing steel reinforcement which consists of either a welded wire fabric or deformed reinforcing steel bars.

1-4. Basic considerations.

Concrete floor slabs on grade are subjected to a variety of loads and loading conditions. The design procedure includes determining slab thickness based on moving live loads and then checking adequacy of slab thickness for stationary live load. The design procedure separately includes determining thickness of slab under wall load. The entire design procedure is based on a working stress concept. Stresses in-duced by temperature gradients and other environ-mental effects are taken into account by the assign-ment of working stresses. Working stresses have been established empirically based on experience gained in roadway and airfield pavement perform-ance data.

1-5. References.

Appendix A contains a list of references used in this document.

2-1

CHAPTER 2

BASIS OF FLOOR SLAB ON GRADE DESIGN

2-1. Stresses. thermal expansion and contraction of the concrete The structural design of a concrete floor slab on grade is primarily controlled by the stresses caused by moving live loads and in some cases the stationary loads. Stresses in floor slabs on grade resulting from vehicular loads are a function of floor slab thickness, vehicle weight and weight distribution, vehicle wheel or track configuration, modulus of elasticity and Poisson*s ratio of concrete, and modulus of subgrade reaction of supporting material. The volume of traffic during the design life is important for fatigue consid-erations. The floor slab design procedure presented The maximum allowable stationary live load is lim-herein is based on limiting the critical tensile stresses ited by both the positive bending moment stress produced within the slab by the vehicle loading, as under the load and the negative bending moment in TM 5-822-6/AFM 88-7, Chap. 1. Correlation stresses occurring at some distance from the load.

studies between theory, small-scale model studies, a. Positive bending moments. Stresses due to and full-scale accelerated traffic tests have shown positive bending moment are relatively simple to that maximum tensile stresses in floor slabs will compute by using Westergaard*s analysis* of elasti-occur when vehicle wheels are tangent to a free cally supported plates. An appropriate safety factor edge. Stresses for the condition of the vehilcle is applied to determine allowable stresses due to wheels tangent to an interiorjoint where the two these loads because environmentally imposed slabs are tied together are less severe than a free stresses must also be accounted for when edge because of the load transfer across the two considering stationary loads.

adjacent slabs. In the case of floor slabs, the design b. Negative bending moments. The effect of can be based on the control of stress at interior negative bending stress is somewhat more difficult joints. Exceptions to this assumption for interior to determine. A slab on an elastic subgrade will joint loading occur when a wheel is placed at the deform under loading somewhat like a damped sine edge at doorways or near a free edge at a wall. curve in which the amplitude or deformation of

2.2 Vehicle-imposed loads. position decreases asymptotically to zero. Thus, For determining floor slab design requirements, mili-tary vehicles have been divided into three general classifications: forklift trucks, other pneumatic and solid tired vehicles, and tracked vehicles. The relative severity of any given load within any of the three classifications is determined by establishing a relationship between the load in question and a standard loading. Floor slab design requirements are then established in terms of the standard load. Other stresses such as restraint stresses resulting from slab and warping stresses resulting from moisture and temperature gradients within the slab, due to their cyclic nature, will at times be added to the moving live load stresses. Provision for these stresses that are not induced by wheel loads is made by safety factors developed empirically from full-scale accelerated traffic tests and from the observed performance of pavements under actual service conditions.

2-3. Stationary live loads.

successive cycles at a distance from the loading there exists some critical aisle width where the damped sine curves from parallel loading areas are in phase and additive. In this situation, the negative bending moment stresses wil become significant and must be considered. Therefore, allowable stationary live loads were established to include the effects of negative moment bending stresses. These calculations are reflected in the tabulated values of allowable stationary live loads.

* Westergaards analysis Is actually for plates on a liquid foundation, sometimes called a Winkler foundation. There Is a distinct difference between the structural behavoir of plates on a liquid and on an elastic foundation. In many textbooks, the term “beam on elastic foundation” Is actually “beam on liquid foundation.”

2-2

2-4. Wall loads. is based on the theory of a beam on a liquid There are situations where a wall is placed on a new thickened slab or- on an existing concrete floor slab on grade. Walls weigh from several hundred to several thousand pounds per linear foot. The design table used for determining thicknesses required under walls is developed by Staab (see Biblio) and foundation subjected to concentrated loads. Three loading conditions are considered: loads at the center of the slab, loads at a joint, and loads at the edge of the slab. The widths of thickened slabs are developed together with the recommended transitions.

3-1

CHAPTER 3

DETERMINATION OF FLOOR SLAB REQUIREMENTS

3-1. Vehicular loads. the drive axle of a forklift truck is normally 87 to 94 The following traffic data are required to determine the floor slab thickness requirements:

— Types of vehicles

— Traffic volume by vehicle type

— Wheel loads, including the maximum single-axle and tandem-axle loading for trucks, forklift trucks, and tracked vehicles

— The average daily volume of traffic (ADV) which, in turn, determines the total traffic volume anticipated during the design life of the floor slab.

For floor slabs, the magnitude of the axle load is of far greater importance than the gross weight. Axle spacings generally are large enough so that there is To aid in evaluating traffic for the purposes of floor little or no interaction between axles. Forklift truck slab design, typical forklift trucks have been divided traffic is expressed in terms of maximum axle load. into six categories as follows:

Under maximum load conditions, weight carried by percent of the total gross weight of the loaded vehicle.

For tracked vehicles, the gross weight is evenly divided between two tracks, and the severity of the load can easily be expressed in terms of gross weight. For moving live loads, axle loading is far more important than the number of load repetitions.

Full-scale experiments have shown that changes as little as 10 percent in the magnitude of axle loading are equivalent to changes of 300 to 400 percent in the number of load repetitions.

3-2. Traffic distribution.

Forklift Truck Forklift Truck Maximum Load Category Maximum Axle Load, kips Capacity, kips

I 5 to 10 2 to 4 II 10 to 15 4 to 6 III 15 to 25 6 to 10 IV 25 to 36 10 to 16 V 36 to 43 16 to 20 VI 43 to 120 20 to 52

When forklift trucks have axle loads less than 5 kips considering each axle as one forklift truck axle of and the stationary live loads are less than 400 approximate weight. For example, a three-axle truck pounds per square foot, the floor slab should be with axle loads of 6, 14, and 14 kips will be designed in accordance with TM 5-809-2/AFM 88- considered as three forklift truck axles, one in 3, Chap. 2. Vehicles other than forklift trucks such Category I and two in Category II. Tracked vehicles as conventional trucks shall be evaluated by are categorized as follows:

Forklift Truck Tracked Vehicles

Category Maximum Bross Weight, kips

I less than 40 II 40 to 60 III 60 to 90 IV 90 to 120

Categories for tracked vehicles may be substituted for the same category for forklift trucks.

w ' 257.876s kh E

TM 5-809-12/AFM 88-3, Chap. 15

3-2

(eq 3-1)

3-3. Stationary live loads. k = the modulus of subgrade reaction, pounds Floor slabs on grade should have adequate structural live loads. Since floor slabs are designed for moving live loads, the design should be checked for stationary live loading conditions. Table 3-1 lists values for maximum stationary live loads on floor slabs. For very heavy stationary live loads, the floor slab thicknesses listed in table 3-1 will control the design. Table 3-1 was prepared using the equation where w = the maximum allowable distributed stationary live load, pounds per square foot s = the allowable extreme fiber stress in tension excluding shrinkage stress and is assumed to be equal to one-half the normal 28-day concrete flexural strength, pounds per square inch per cubic inch h = the slab thickness, inches E= the modulus of elasticity for the slab

(assumed to equal 4.0 x 106 pounds per square inch)

The above equation may be used to find allowable loads for combinations of values of s, h, and knot given in table 3-1. Further safety may be obtained by reducing allowable extreme fiber stress to a smaller percentage of the concrete flexural strength have been presented by Grieb and Werner, Waddell, and Hammitt (see Biblio). The selection of the modulus of subgrade reaction for use in table 3-1 is discussed in paragraph 4-2d. The design should be examined for the possibility of differential settlements which could result from nonuniform subgrade support.

Also, consideration of the effects of long-term overall settlement for stationary live loads may be necessary for compressible soils (see TM 5-818- 1/AFM 88-3, Chap. 7).

k/100.

3-3

Table 3-1. Maximum allowable stationary live load

Slab lb/ft for These Flexural Thickness Strengths of Concrete

Stationary Live Load w in inches 550 lb 600 lb 650 lb 700 lb h in in in in2 2 2 2

6 868 947 1,026 1,105

7 938 1,023 1,109 1,194

8 1,003 1,094 1,185 1,276

9 1,064 1,160 1,257 1,354

10 1,121 1,223 1,325 1,427

11 1,176 1,283 1,390 1,497

12 1,228 1,340 1,452 1,563

14 1,326 1,447 1,568 1,689

16 1,418 1,547 1,676 1,805

18 1,504 1,641 1,778 1,915

20 1,586 1,730 1,874 2,018

NOTE: Stationary live loads tabulated above are based on a modulus of subgrade reaction (k) of 100 lb/in . Maximum allowable stationary live loads for other3 moduli of subgrade reaction will be computed by multiplying the above—tabulated loads by a constant factor. Constants for other subgrade moduli are tabulated below.

Modulus of 25 50 100 200 300 Subgrade reaction Constant factor 0.5 0.7 1.0 1.4 1.7

For other modulus of subgrade reaction values, the constant values may be found from the expression

3-4

3-4. Wall loads. 3-5. Unusual loads.

Floor slabs on grade should have adequate thickness Information regarding floor slab requirements for to carry wall loads. Tables 3-2 and 3-3 show the special purpose ordnance, engineer, or transport minimum thicknesses of thickened slabs for various vehicles producing loads significantly greater than wall loads. The equations used to compute these those defined herein should be requested from values are included in appendix B. When slab Headquarters, Department of the Army (HQDA) thickness required for wall loads exceeds that (DAEN-ECE-G) Washington, DC 20314-1000 or required for moving live loads or stationary live Headquarters, Air Force Engineering and Services loads, the slab will be thickened in accordance with Center (DEMP), Tyndall MB, Fla. 32403.

figure 3-1. The safety factor for the design was considered by using a reduced allowable tensile stress of the concrete, o , which was computedt using the equation o = 1.6 /f’ , where f' is thet c c ultimate compressive strength of the concrete. If wall loads exceed the tabulated values shown in table 3-2, separate wall footings are suggested.

Figure 3-la shows the widths of thickened slabs when the interior wall loads are near the slab center.

A recommended transition is also shown. The thickened slab width is determined by the same theory as the wall loads. The slab under the wall is widened to the point where the stress in the thinner slab section does not exceed the allowable tensile stress of 1.6 /f’ . Figure 3-1b shows a slab loadedc near a keyed or doweled edge. Figure 3-lc shows a recommended slab thickening for a slab loaded near a free edge. The width of the thickened edge varies depending upon the width of the wall.

100/k.

9 f ) c

TM 5-809-1/AFM 88-3, Chap. 15

3-5

Table 3-2. Minimum thickness of thickened floor slab for wall load near center of slab or near keyed or doweled joint

Thickness of Slab Line Load Capacity, P, (lb/lin ft) Thickened Floor Flexural Strength of Concrete (lb/in )a 2

Slab, t , (inches) 550 600 650 700e

4 425 455 485 510 5 565 600 640 675 6 710 755 805 850 7 860 920 975 1,030 8 1,015 1,080 1,150 1,215 9 1,175 1,255 1,330 1,410 10 1,340 1,430 1,520 1,605

NOTE: The allowable wall loads are based on a modulus of subgrade reaction (k) of 100 pounds per cubic inch. The thickness of the thickened slab will be computed by multiplying the above thick— nesses by a constant factor. Constants for other subgrade moduli are tabulated below.

Modulus of 25 50 100 200 300 Subgrade reaction k Constant factor 1.3 1.1 1.0 0.9 0.8

For other modulus of subgrade reaction values the constant values may be found from

For this application the flexural strength of concrete wasa assumed equal to where f’ is the specified compressivec strength of concrete (lb/in ).2

3-6

Table 3-3. Maximum allowable wall load near free edge

Thickness of Slab Line Load Capacity, P, (lb/lin ft) Thickened Slab, t Flexural Strength of Concrete (lb/in )e a 2

(inches) ) 550 600 650 700

4 330 355 375 395

5 435 465 495 525

6 550 585 620 660

7 665 710 755 800

8 785 840 890 945

9 910 975 1,035 1,090

10 1,040 1,110 1,180 1,245

3-7

4-1

CHAPTER 4

SITE INVESTIGATION

4-1. General c. Exploration and classification. If field recon- Once the floor slab load capacity requirements have been established, an investigation of the existing conditions at the site must be made. Conditions to be considered include an investigation of the subgrade, climatic conditions, the need for and availability of base course materials, and the concrete strength properties likely to be encountered in the locale.

4-2. Subgrade conditions.

a. Importance of subgrade conditions. The sub-grade provides a foundation for supporting the floor slab and base courses. As a result, the required floor slab thickness and the performance obtained form the floor slab during its design life will depend in a large part, on the uniformity and bearing capacity of the subgrade. It is desirable, if economically feasible, to thoroughly investigate the subgrade to assess the maximum support potential for the particular sub-grade. In unheated structures, the possibility of frost heave emphasizes the importance of uniformity of soil conditions under the floor slab.

b. Initial investigation. Preliminary investigations of subgrade conditions at the site of proposed construction should be performed to determine the engineering characteristics of the subgrade soils and the extent of any peculiarities of the proposed site.

The general suitability of the subgrade soils is to be based on classification of the soil, moisture density relationships, expansive characteristics, susceptibil-ity to pumping, and susceptibility to detrimental frost action. A careful study of the service history of existing floor slabs on similar subgrade materials in the locality of the proposed site should be made.

Factors such as ground water, surface infiltration, soil capillarity, topography, rainfall, drainage condi-tions, and the seasonal change of such factors also may affect the support rendered by the subgrade.

naissance and analysis of existing subsurface infor-mation are insufficient to provide the necessary data for floor-slab design, an exploration program should be initiated according to provisions of TM 5-81 8-1/ AFM 88-3, Chap. 7. All soils should be classified in accordance with MIL-STD-619. Sufficient investigations should be performed at the proposed site to facilitate the classification of all soils that will be used or removed during construction; other pertinent descriptive information should also be included.

d. Performance data. For the design of rigid floor slabs in areas where no previous experience regard-ing floor slab performance is available, the modulus of subgrade reaction k to be used for design purposes is determined by the field plate-bearing test. A description of the procedure to be followed for this test and the method for evaluating test results are given in MIL-STD-621. Where performance data from existing floor slabs on grade are available, adequate values for k usually can be estimated on the basis of soil type, drainage conditions, and frost conditions that prevail at the proposed site. Table 4-1 lists typical values of modulus subgrade reaction for various soil types and moisture contents. Values shown may be increased slightly if the density is greater than 95 percent maximum CE 55 density, except that a maximum of 500 pounds per cubic inch will be used for design. These values should be considered as a guide only, and their use in lieu of the field plate-bearing test is left to the discretion of the engineer.

The fact that the materials are shown in the table does not indicate suitability for use. Suitability must be determined for the particular job conditions.

4-2

Table 4-1. Typical values of modulus of subgrade reaction

Modulus of Subgrade Reaction, k, in lb/in3 for Moisture Contents of 1 5 9 13 17 21 25 to to to to to to to Over

Types of Materials 4% 8% 12% 16% 20% 24% 28% 29%

Silts and clays -- 175 150 125 100 75 50 25 Liquid limit > 50

(OH, CH, MH)

Silts and clays -- 200 175 150 125 100 75 50 Liquid limit < 50

(OL, CL, ML)

Silty and clayey 300 250 225 200 150 — — --sands (SM & SC)

Gravelly sands 300+ 300 250 — — — — --

(SW & SP)

Silty and clayey 300+ 300+ 300 250 — — — --gravels (GM & GC)

Gravel and sandy 300+ 300+ — — — — — --gravels (GW & GP)

NOTE: k values shown are typical for materials having dry densities equal to 90 to 95 percent of the maximum CE 55 density. For materials having dry densities less than 90 percent of maximum CE 55 density, values should be reduced by 50 lb/in , except that a k of 25 lb/in will3 3 be the minimum used for design.

4-3

4-3. Environmental conditions. economical means of maintaining a stable thermal

a. Freezing and thawing. Special additional design considerations and measures are necessary where freezing and thawing may occur in underlying soils. The effects of such occurrences, which are termed “frost action,” include surface heaving during freezing and loss of bearing capacity upon thawing. Detrimental frost action is the result of the development and/or thawing of segregated ice in underlying soils. Potential difficulties from frost action exist whenever a source of water is available to a frost-susceptible soil which is subject to subfreezing temperatures during a portion of the year. Conditions necessary for the development of ice segregation in soils together with a description of the ice segregation process and the detrimental effects of frost action are given in TM 5-818- 2/AFM 88-6, Chap. 4.

b. Cold storage facilities. A somewhat different problem is encountered in cold storage facilities where a structure in contact with the ground is a. General. For a given water-cement ratio, the maintained at subfreezing temperature. Thus, frost concrete strength likely to be obtained in a given action under such structures is a long-term rather locale depends primarily on the aggregate sources than a seasonal phenomenon, and deep frost available. Maximum particle size and quality of the penetration will eventually result, even in areas coarse aggregate will have a pronounced effect on where subfreezing ground temperatures are not concrete strength as will the gradation of the naturally experienced, unless insulation or blended coarse and fine aggregate. In general, provisions for circulation of warm air beneath the aggregates of the bankrun variety, as opposed to slab are provided in design. Recommended as a crushed aggregates, will produce a lower-strength reference is American Society of Heating, concrete due to particle shape. Specified concrete Refrigerating, and Air-Conditioning Engineering strength should be sufficient to provide high wear ASHRAE Handbook and Product Directory, resistance properties, constructability, and a Equipment, and Applications, (see Biblio). It should reasonably high flexural stress to attain the greatest be kept in mind that insulation may merely slow economy in the design. A study should be made of frost penetration. It does not prevent heat flow. the strengths likely to be encountered, since

c. Permafrost. Since construction alters the ex- specifying an unusually high-strength concrete mix isting thermal regime in the ground, an additional may result in a higher material cost for the project.

problem is encountered in regions where heat flow b. Traffic types. The minimum concrete compres-from the facility may result in the progressive thaw- sive strength for floors subjected to pneumatic tired ing of perennially frozen ground (permafrost). Ther- traffic will be 4,000 pounds per square inch; for mal degradation of permafrost which contains floors subjected to abrasive traffic such as steel masses of ice will result in subsidence as well as wheels, the minimum concrete compressive strength reduction in bearing capacity. Both may be severe. will be 5,000 pounds per square inch.

The most widely employed, effective, and regime in permafrost under slabs-on-grade is by means of a ventilated foundation. Provision is made for ducted circulation of cold winter air between the insulated floor and underlying ground. The air circulation serves to carry away the heat both from the foundation and the overlying building, freezing back the upper layers of soil which were thawed the preceding summer. The characteristics of permafrost and engineering pinciples in permafrost regions are described in TM 5-852-1/AFM 88-19, Chap. 1, and

TM 5-852-4.

d. Applicable technical manuals. Where freezing and/or thawing may occur in underlying soils, slab design will be in accordance, as applicable, with TM 5-818-2/AFM 88-6, Chap. 4 and TM 5-852-4.

Thermal computatio procedures are detailed in TM 5-852-6/ AFM 88-19, Chap. 6.

4-4. Concrete strength.

5-1

CHAPTER 5

DESIGN PROCEDURE

5-1. General. which expresses varying axle loads and traffic Once the floor-slab design requirements have been established, i.e., the type of loadings, including wall loads and both stationary live and moving live loads, the requirements are translated into meaningful design data. These design data are then compared with the existing condition data, and a floor slab design is evolved. The design procedure covers sub-grade conditions, steel reinforcing, and various de-tails such as jointing.

5-2. Floor slab loads.

a. Traffic loadings. In order to satisfy require-ments of different types of vehicles and traffic vo-lumes, all Category I, II, and III traffic has been expressed in terms of equivalent operations of a basic axle loading. The basic loading was assumed to be an 1 8,000-pound single-axle load with two sets of dual wheels spaced 58-1/2 inches apart with 13-1/2 inches between dual wheels. It should be noted that the basic loading was arbitrarily selected to provide a reasonable spread in the loadings and traffic volumes likely to be encountered under normal conditions. A design index (DI) was devised volume in terms of relative severity. The DI ranges from 1 to 10 with the higher number indicating a more severe design requirement. The basic loading described above was used to assign and rank the Dl*s. More information concerning the DI can be found in TM 5-822-6/AFM 88-7, Chap. 1. Table 5- 1 shows the DI*s for various traffic volumes. Thick-ness requirements for floor slabs which contain only temperature reinforcement for the ten DI*s are shown in figure 5-1. The floor-slab thickness requirements are a function of concrete strength and subgrade modulus and DI. Larger forklifts having axle loads greater than 25 kips are treated separately. The required slab thickness for pavements designed for these loads are not significantly affected by vehicles having axle loads less than 25 kips (trucks, cars, buses, and small forklifts). These light loads are therefore ignored in determining requirements for pavements carrying axle loads greater than 25 kips. The thickness requirements for these loads are shown in figure 5-2.

Table 5-1. Traffic categories for design index

Maximum Operations Design Per Day Over 25 Years Load Index

50 10-kip axle-load forklift truck 4

250 10-kip axle-load forklift truck 5 10 15-kip axle-load forklift truck

250 10-kip axle-load forklift truck 7 100 15-kip axle-load forklift truck

250 15-kip axle-load forklift truck 8 5 25-kip axle-load forklift truck

5-2

5-3 ho '

1.4 h 1.4 & 0.0063

Ef hs

1.4

TM 5-809-12/AFM 88-3, Chap. 15

5-4

(eq 5-1)

b. Stationary live loads. Stationary live loads are pavement design in equation 5-1:

expressed in terms of maximum allowable pounds per square foot. These loadings are given in table 3-

1. The method used to determine the allowable loads is based on the concrete flexural strength, the slab thickness, and the modulus of subgrade reaction. Entering table 3-1 with the flexural strength and the slab thickness, the allowable stationary live load can be selected. Based on the modulus of subgrade reaction, the load is adjusted using the constant factor given in the note (table 3- 1).

c. Wall loads. Stationary-partition loads are expressed in terms of pounds per linear foot. These loadings are given in table 3-2. The method used to determine thickness, t , of the thickened floor slab isc based on the concrete flexural strength, the load, and the modulus of subgrade reaction. Entering table 3-2 with the flexural strength of the concrete and the load, the concrete thickness is selected, based on a modulus of subgrade reaction of 100 pci.

The thickness is adjusted using the constant factor given in the note (table 3-2), for other subgrade moduli.

d. Design procedures for stabilized foundations.

(1) Soil stabilization or modification. Soils that have been treated with additives such as cement, lime, fly ash, or bitumen are considered to be either stabilized or modified. A stabilized soil is one that shows improvement in load-carrying capability and durability characteristics. A modified soil is one that shows improvement in its construction characteristics but which does not show an increase in the strength of the soil sufficiently to qualify as a stabilized soil. The principal benefits of soil modification or stabilization include a stable all-weather construction platform and a reduction of rigid pavement thickness requirements when applicable, swell potential, and susceptibility to pumping and strength loss due to moisture.

(2) Requirements. The design of the stabilized or modified layers will follow TM 5-822- 4, and TM 5-818-2/AFM 88-6, Chap. 4. To qualify as a stabilized layer, the stabilized material must meet the unconfined compressive strength and durability requirements in TM 5-882-4; otherwise, the layer is considered to be modified.

(3) Thickness design. The thickness require-ments for a rigid pavement on a modified soil foundation will be designed as if the layer is unbounded using the k value measured on top of the modified soil layer. For stabilized soil layers, the treated layer will be considered to be a low-strength base pavement and the thickness determined using the following modified partially bonded rigid overlay where h = thickness of rigid pavements overlayo required over the stabilized layer, inches h = thickness of rigid pavement from design chart (fig. 5-1) based on k value of unbound material, inches

E = flexural modules of elasticityf (as determined by ASTM C 78) h = thickness of stabilized layer, inchess

e. Design Examples. Example design problems can be found in appendix C.

5-3. Subgrade.

a. Compaction. Compaction improves stabiliity of most subgrade soils and provides a more uniform foundation for the floor slabs or base course. Method 100 of MIL-STD-621, Compaction Effort CE 55, should be used to determine the compaction characteristics of the subgrade soils.

During construction, prolonged exposure of the subgrade to the atmosphere may allow overwetting or and drying therefore should not be allowed.

b. Cut sections. With the exception of areas of special soil, the top 6 inches of subgrade in cut sections should be scarified and moistened to approximately optimum moisture content and compacted. Cohesive subgrade soils should be compacted to a minimum of 90 percent of CE 55 maximum density and cohesionless soils to a minimum percent of CE 55 maximum density.

c. Fill sections. With the exception of fill com-posed of special soils, all fills composed of cohesive materials should be compacted to minimum of 90 percent of CE 55 maximum and all fills composed of cohesionless materials should be compacted to a minimum of 95 percent of CE 55 maximum density.

Some adjustment., for compaction requirements may be necessary ;for fills of expansive soils..

d. Cut-to-fill sections. When a rigid floor slab is located partially on a fill area and partially on a cut area, the compaction. requirements set forth in the preceding paragraphs should be followed. The depth of subgrade compaction in the cut area should be increased to 12 inches.

5-5

e. Nonuniformity. Where it is not possible to create uniform subgrade conditions by the methods described herein, the slab design can be varied throughout the project to maximize economy. Con-crete flexural strength, percent reinforcing steel, and slab thickness can all be adjusted to provide a design which is balanced in terms of service life. The specific combinations to be used will depend upon local conditions and costs, and selection of design alternatives is left to the discretion of the design engineer.

f. Special soils. Although compaction increases the stability and strength of most soils, some soil types show a marked decrease in stability when scarified, worked, and rolled. Also, there are some soils that shrink excessively during dry periods and expand excessively when allowed to absorb moisture. In general, these are inorganic clays of relatively high plasticity usually classified as CH soils. Special types of soils are discussed in TM 5- 825-2/AFM 88-6, Chap. 2, TM 5-818-1/AFM 88-3, Chap. 7, and TM 5-818-7.

g. Back filling. Special care should be exercised in backfill areas around walls and columns to ensure compliance with compaction requirements outlined in the above paragraphs. Backfilling around walls and columns should be performed with pneumatic tampers, gasoline-powered tampers, and other mechanized hand-operated devices. Soil moisture content and lift thickness should be carefully con-trolled to ensure that compaction requirements are met through the full depth of the backfill.

h. Treatment of unsuitable materials. Soils desig-nated as unsatisfactory for subgrade use by MIL-.

STD-619 should be removed and replaced. The depth to which such undesirable soils should be removed depends on the soil type, drainage conditions, type of material stored, magnitude of tolerable differential settlement, and depth of freezing-temperature penetration. The depth of removal and replacement should be determined by the engineer on the basis of judgement and previous experience and with due consideration of the traffic to be served as well as the costs involved. In some instances, unsatisfactory or undesirable soils may be improved economically by stabilization with such materials as cement, fly ash, lime, or certain chemical additives whereby the characteristics of the composite material become suitable for use as subgrade. Criteria for soil stabilization are given in TM 5-822-4. Subgrade stabilization, however, should not be attempted unless the cost reflects corresponding savings in base course, floor slabs, or drainage facilities construction and is approved by HQDA (DAEN-ECE-G) Washington, DC 2031 4-1 000 or Headquarters, Air Force Engineering Services Center (DEMP), Tyndall AFB, Fla. 32403.

5-4. Base courses.

a. Requirements. Base courses may be required under rigid floor slabs to provide protection against detrimental frost action, drainage, a suitable working platform for the construction operation during adverse weather conditions, and additional support to the floor slab. In any of the above-mentioned applications for base courses, an economic study is required to determine base course requirements in floor-slab design. The economic study will typically include costs of base course materials such as hauling and required floor-slab thickness with and without base course.

Consideration should also be given to the use of the floor slab, i.e., what material is to be stored and what operations are likely to occur on the floor slab.

These considerations will also have an impact on whether to include a base course.

b. Compaction. Where base courses are used, the base-course materials should be compacted in accordance with the criteria given above. With this in mind, note that compaction of thin base courses placed on yielding subgrades to high densities is difficult.

c. Drainage. Adverse moisture conditions result-ing from high water table and subsoils subject to capillary action may cause damage to floor covering and stored material. If the subgrade soils provide for movement of water by capillary flow (CH, CL, MH, and ML types) and the ground-water table is less than 5 feet from the final grade, a minimum thickness of 6 inches of free-draining base course will be required. Base courses for drainage will not be required under conditions of deep ground-water table. Positive drainage is to be provided to ensure against water being trapped beneath the pavement.

The floor should be protected against the migration of water vapor through the slab…