SABP-Q-008 Aramco Civil Practices

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Best Practice

SABP-Q-008 28 February 2005 Design of Concrete Masonry Walls/Buildings

DESIGN OF CONCRETE MASONRY WALLS/BUIDLINGS

Developed By: Hisham Abu-Adas

Civil Engineering Unit / M&CED Consulting Services Department

Document Responsibility: Onshore Structures SABP-Q-008 Issue Date: 28 February 2005 Next Planned Update: 1 March 2009 Design of Concrete Masonry Walls/Buildings

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DESIGN OF CONCRETE MASONRY WALLS/BUILDINGS

Table of Contents Page 1 Introduction.........................................................................................................4

1.1 Purpose.....................................................................................................4

1.2 Scope.........................................................................................................4

1.3 Disclaimer ................................................................................................4

1.4 Conflicts with Mandatory Standards....................................................5

2 References............................................................................................................5

2.1 Saudi Aramco Standards .......................................................................5

2.2 Industry Codes and Standards ..............................................................5

3 General.................................................................................................................6

4 Masonry ...............................................................................................................7

5 Design Loads & Load Combinations ................................................................8

6 Notation................................................................................................................9

7 Allowable Stresses.............................................................................................10

8 Wall Reinforcement ..........................................................................................12

9 Design Properties .............................................................................................13

ATTACHMENTS:

Attachment 1:

Table 5: Area of Steel ....................................................................................... 15

Table 6: Area of Steel Per Foot of Wall (SI) ..................................................... 15

Table 7: Area of Steel Per Foot of Wall (Metric) .............................................. 16


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Attachment 2: Masonry Wall Design - Example 1 (Manual Calculations) ............17

Attachment 3: Masonry Wall Design - Ex. 1 (In-house Developed Spreadsheet)...21


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1 Introduction

1.1 Purpose

The purpose of this practice is to provide the engineer and designer with guidelines for design of concrete masonry walls for use by Saudi Aramco engineers and engineers working on Saudi Aramco projects.

1.2 Scope

This design guide defines the minimum requirements for the analysis and design of reinforced load bearing masonry walls for buildings and structures located in process industry facilities at Saudi Aramco sites. It covers general design philosophy and requirements to be used in the analysis and design of load bearing masonry walls subjected to a combination of axial uniform dead and live loads, eccentric uniform vertical dead and live loads, and lateral loads due to wind or seismic forces. Section 2.0 of this instruction includes reference codes and Saudi Aramco standards. The walls presented in this guideline covers load bearing walls subject to axial compressive load and bending moment.

1.3 Disclaimer

The material in this Best Practices document provides the most correct and accurate design guidelines available to Saudi Aramco which complies with international industry practices. This material is being provided for the general guidance and benefit of the Designer. Use of the Best Practices in designing projects for Saudi Aramco, however, does not relieve the Designer from his responsibility to verify the accuracy of any information presented or from his contractual liability to provide safe and sound designs that conform to Mandatory Saudi Aramco Engineering Requirements. Use of the information or material contained herein is no guarantee that the resulting product will satisfy the applicable requirements of any project. Saudi Aramco assumes no responsibility or liability whatsoever for any reliance on the information presented herein or for designs prepared by Designers in accordance with the Best Practices. Use of the Best Practices by Designers is intended solely for, and shall be strictly limited to, Saudi Aramco projects. Saudi Aramco® is a registered trademark of the Saudi Arabian Oil Company. Copyright, Saudi Aramco, 2005.


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1.4 Conflicts with Mandatory Standards

In the event of a conflict between this Best Practice and other Mandatory Saudi Aramco Engineering Requirement, the Mandatory Saudi Aramco Engineering Requirement shall govern.

2 References

This Best Practice is based on the latest edition of the applicable codes, standards, specifications, and references below, unless otherwise noted. Short titles will be used herein when appropriate.

2.1 Saudi Aramco Standards

Saudi Aramco Engineering Standards (SAES)

SAES-A-204 Preparation of Structural Calculations

SAES-M-001 Structural Design Criteria for Non-Building Structures

SAES-M-100 Saudi Aramco Building Code

SAES-Q-001 Criteria for Design and Construction of Concrete Structures

SAES-Q-005 Concrete Foundations

Saudi Aramco Materials System Specification (SAMSS)

09-SAMSS-016 Concrete Masonry Units and Concrete Building Bricks

2.2 Industry Codes and Standards

American Concrete Institute (ACI)

ACI 530-02 Building Code Requirements for Masonry Structures

American Society of Civil Engineers (ASCE)

ASCE 5-02 Building Code Requirements for Masonry Structures

International Code Council (ICC)

IBC 2003 International Building Code, 2003 Edition


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The Masonry Society (TMS)

TMS 402-02 Building Code Requirements for Masonry Structures

3 General

3.1 The design of load bearing masonry wall shall be in accordance with the requirements of Saudi Aramco Engineering Standard SAES-M-100 and ACI 530-02/ASCE 5-02/TMS 602-02, and this guideline.

3.2 Concrete building load bearing concrete masonry units shall be in accordance with 09-SAMSS-016.

3.3 The mortar shall be type S Mortar Cement as specified in Tables No. 2103.7(2) of IBC 2003. The specified compressive strength of mortar shall not be less than 1800 psi (12.4 MPa).

3.4 The minimum compressive strength of concrete masonry units shall be 1900 psi. The corresponding specified compressive strength of masonry f ′m shall be limited to a maximum of 1500 psi as per Table No. 2105.2.21.2 0f IBC 2003.

3.5 The use of full stresses by calling for special inspection is not allowed. The allowable stresses for masonry shall be reduced by half.

3.6 The design of masonry structure shall comply with the provisions of Chapter 2 “Allowable Stress Design” of ACI 530-02.

3.7 The load bearing walls shall be designed as reinforced masonry. The minimum vertical reinforcement shall be #4 bars at 4 ft spacing (12 mm diameter bars at 1.2 meters spacing). The minimum horizontal joint reinforcement shall be 2 #5 mm diameter longitudinal truss bars placed at 16-inch centers.

3.8 Vertical reinforcement shall be provided at each side of openings and at corners. Also, horizontal masonry beams or lintels shall be provided to distribute concentrated loads at the roof and above and below openings.

3.9 The structural calculations shall be prepared in accordance with the requirements of SAES-A-204.

3.10 A strip of wall one-foot in length will be assumed in the analysis and design, and all forces per linear foot basis. The design dead and live load moments at mid height will be assumed to equal half (½) of moments at top of wall. The wall will be assumed pinned at top and bottom. Wind or seismic moments will be added to dead and live load moments at mid height of wall.


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4 Masonry

4.1 The most common hollow concrete masonry units used in the design are 6″, 8″, 10″ and 12″ widths and 16″ lengths. These are nominal sizes assuming 3/8″ grout and masonry units standard blocks manufactured in accordance with ASTM C90.

4.2 The average weight of Completed Walls (psf) and Equivalent Solid Thickness (inches) assuming weight of grout equals 140 pcf for Normal Weight block (135 pcf) shall be as listed in Table 1 below:

TABLE 1 – Average Wt. of Masonry Walls & Equivalent Solid Thickness

*Weight of Wall (psf) **Equivalent Solid Thickness (inches)

Wall Thickness 6″ 8″ 10″ 12″ 6″ 8″ 10″ 12″

Solid Grouted Wall 63 84 104 133 5.6 7.6 9.6 11.6

16″ o.c. 52 66 86 103 4.5 5.8 7.2 8.5

24″ o.c. 48 61 78 94 4.1 5.2 6.3 7.5

32″ o.c. 47 58 74 89 4.0 4.9 5.9 7.0

40″ o.c. 46 56 72 86 3.8 4.7 5.7 6.7

Vertical

Cores

Grouted

at

48″ o.c. 45 55 70 83 3.7 4.6 5.5 6.5

No Grout in Wall 37 42 47 62 3.4 4.0 4.7 5.5

* The above table gives the average weight of completed walls of various thicknesses in pounds per square foot of wall face area.

** Equivalent solid thickness (EST) means the calculated thickness of the wall if there were no hollow cores, and is obtained by dividing the volume of the solid material in the wall by the face area of the wall.


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4.3 The radius of gyration (r) for concrete masonry units shall be as listed in Table 2 below:

TABLE 2 – Radius of Gyration (r) for Concrete Masonry Units

r = ( I/Ae)1/2

5 Design Loads & Load Combinations

5.1 Vertical loads shall include the dead loads of the roof and wall as well as the roof live load. Eccentricity of vertical loads shall be considered.

5.2 Horizontal loads due to wind or seismic shall be combined singly with dead and live loads.

5.3 Load Combinations: Buildings and structures shall be designed to resist the most restrictive of the following combination of loads:

D (a)

D + L (b)

D + L + (W or E) (c)

D + W (d)

0.9 D + E (e)

Nominal Width of Wall (inches) Grout Spacing

(inches) 6 8 10 12

Solid Grouted 1.62 2.19 2.77 3.34

16 1.79 2.43 3.04 3.67

24 1.87 2.53 3.17 3.82

32 1.91 2.59 3.25 3.91

40 1.94 2.63 3.30 3.97

48 1.96 2.66 3.33 4.02


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where:

D = Dead load

L = Live Load

W = Wind Load

E = Earthquake Load

5.4 Seismic design requirements shall be in accordance with Section 1.13 of ACI 530-02. Seismic design category classification shall be as defined in Section 9.4.2 of ASCE 7-02.

5.5 The allowable stresses and allowable loads are permitted to be increased by one-third when considering load combinations (c), (d), or (e).

6 Notation


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7 Allowable Stresses

7.1 Steel Reinforcement:

Tension: The allowable tensile stress in reinforcement shall not exceed 24,000 psi (165.5 MPa) for Grade 60 reinforcement.

Compression: The compressive resistance of steel reinforcement shall be neglected unless lateral reinforcement is provided in compliance with the requirements of Section 2.1.6.5 of ACI 530-02. The compressive stress in reinforcement shall not exceed 24,000 psi (165.5 MPa) for Grade 60 reinforcement.


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7.2 Axial compression and flexure:

7.2.1 The compressive stress in masonry due to flexure or due to flexure in combination with axial load shall not exceed (1/3) f ′m provided the calculated compressive stress due to axial load component, fa, does not exceed the allowable stress, Fa given by Eq. (2-12) or (2-13) of ACI 530-02 and as shown below:

7.2.2 Members subjected to combined axial compression and flexure shall be designed to satisfy Eq. (2-10) below:

7.2.3 Axial tension and flexural tension:

Axial tension and flexural tension shall be resisted entirely by steel reinforcement.

7.3 Shear in Flexural Members:

Where shear reinforcement is provided in accordance with Section 2.3.5.3 of ACI-530-02 to resist all of the calculated shear, the calculated shear stress, fv, shall not exceed Fv, where Fv is determined as follows:


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Where reinforcement is not provided to resist all of the calculated shear, fv shall not exceed Fv, where:

The calculated shear stress in the masonry shall be determined by the relationship:

8 Wall Reinforcement

All load bearing walls, shear walls and walls transmitting flexural loads shall be reinforced with both vertical and horizontal reinforcement. The sum of the areas of horizontal and vertical reinforcement shall be at least 0.002 times the gross cross-sectional area of the wall, and the minimum area of reinforcement in either direction shall not be less than 0.0007 times the gross cross-sectional area of the wall. However, the minimum vertical reinforcement shall be #4 bars at 4 ft spacing (12 mm diameter bars at 1.2 meters spacing). The minimum horizontal joint reinforcement shall be 2 #5 mm diameter longitudinal truss bars placed at 400 mm (16-inch) centers."

• Effective Depth, d, in Masonry Unit Wall:

TABLE 3 - Steel in Center of cell, Block

Nominal Thickness (inches)

Actual Thickness (t) (inches)

d (inches)

6 5 5/8 2.75

8 7 5/8 3.75

10 9 5/8 4.75

12 11 5/8 5.75


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TABLE 4- Steel Place for Maximum d

Nominal Thickness (inches)

Actual Thickness (t) (inches)

Max. d (inches)

6 5 5/8 2.75

8 7 5/8 5.25

10 9 5/8 7.25

12 11 5/8 9.00

9 Design Properties

The following design properties/parameters shall be used for the design of load bearing walls:

Es = 29,000,000 psi for grade 60 reinforcing steel

Em = 750 f’m = 750 x 1500 psi = 1,125,000 psi

n = Es / Em

Radius of gyration r (refer to TABLE 2)

p = As / bd

k = [(np)2 + 2np]1/2 – np

j = 1 – k/3

fa = Ptot./A = Ptot./ (b x t) Equivalent Solid Thickness t = 7.2 in (TABLE 1)

fb = (M/bd2) x (2/kj) Actual Bending Stress


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Masonry: fb = (M/bd2) x (2/jk)

Steel: fs = (M/bd2) x (1/jp) Revision Summary 28 February 2005 New Saudi Aramco Best Practice.


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Attachment 1 – Design Aids

TABLE 5 - AREA OF STEEL IMPERIAL

Bar Size Area ( in2) Area ( mm2) #3 0.11 71 #4 0.20 129 #5 0.31 200 #6 0.44 284 #7 0.60 387 METRIC

Bar Size Area ( in2) Area ( mm2) 10 mm 0.122 79 12 mm 0.175 113 16 mm 0.312 201 20 mm 0.487 314

TABLE 6 - AREA OF STEEL PER FT OF WALL (As) - in2 / ft IMPERIAL Bar Size Bar Spacing (in) # 3 #4 #5 #6 #7 8 0.165 0.300 0.465 0.660 0.900 16 0.083 0.150 0.233 0.330 0.450 24 0.055 0.100 0.155 0.220 0.300 32 0.041 0.075 0.116 0.165 0.225 40 0.033 0.060 0.093 0.132 0.180 48 0.028 0.050 0.078 0.110 0.150


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TABLE 7 - AREA OF STEEL PER FT OF WALL (As) - in2 / ft METRIC BARS Bar Size Bar Spacing (in) 10 mm 12 mm 16 mm 20 mm 8 0.183 0.263 0.468 0.731 16 0.092 0.131 0.234 0.365 24 0.061 0.088 0.156 0.244 32 0.046 0.066 0.117 0.183 40 0.037 0.053 0.094 0.146 48 0.031 0.044 0.078 0.122


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Attachment 2: Masonry Wall Design – Example 1 (Manual Calculations)

Design (Partially Grouted) Load Bearing Masonry Wall: Building Dimensions: Width = 40 ft Length = 50 ft Height = 16.4 ft (5 meters)

GENERAL INFORMATION: Given: Wall Height = 16.40 ft f’m = 1500 psi (Based on Type S Mortar, Compressive Strength of Masonry unit = 1900 psi) Per Table No. 2105.2.2.1.2 (IBC 2003) Fs = 24,000 psi (Grade 60 Steel) Per ACI 530-02 Sect. 2.3.2.1 Wall Thickness = 10 inch (no special inspection) Rebar Size = #4 @ 16”

H = 16.4 ft WL = 20 psf

P

Rv

Rh

Rh


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Depth of rebar d = 4.75 inch (see TABLE 3) Seismic Zone Factor 0 Duration factor 1.33 for wind Load Wall Equivalent Solid Thickness = 7.200 inch (per TABLE 1) Wind Load = 20 psf Roof DL = 110 psf Roof LL = 20 psf

Step 1: Calculate Loads Dead Load = 110 psf x 20 ft = 2,200 #/ft Live Load = 20 psf x 20 ft = 400 #/ft Wind Load = 20 psf Weight of Wall at Mid-height = 86 psf x 16.4 ft x 0.5 = 705.2 #/ft Total Load Pt = 2,200 + 400 + 705.2 = 3,305.2 #/ft Moment due to W.L.: M = wl2/8= 20 psf x (16.4)2 / 8 = 672.4 #-ft/ft = 8,068.80 #-in/ft Shear Vmax = 20 psf x 16.4 x 0.5 = 164 #/ft

Step 2: Calculate Maximum Allowable Stress:

Em = 750 f’m = 750 x 1500 psi = 1,125,000 psi

Es = 29,000,000 psi for reinforcing steel

n = Es / Em = 29,000,000 / 1,125,000 = 25.778

h = 16.4 ft = 16.4 ft x 12 = 196.8 inch

r = (I/A)1/2 = 3.04 in (ref. Table 2)

h/r = 196.8 / 3.04 = 64.74 < 99 Use Eq. 2-12 (ACI 530-02)

Allowable Masonry Axial Stress Fa:

Fa = 0.25 x 1,500 [(1- {196.8/(140 x 3.04)2} = 294.82 psi x 0.5 (no Sp. Insp.)

Fa = 147.41 psi


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Allowable Masonry Bending Stress Fb:

Fb = 0.333 x 1,500 x 0.5 = 249.75 psi

Allowable Steel Bending Stress Fs:

Fs = 24,000 psi

Step 3: Calculate Maximum Actual Block Wall Stress at Mid-Height:

Note: Axial load is carried mainly by masonry block, steel does not carry compression load.

fa = Ptot./A = Ptot./ (b x t) Equivalent Solid Thickness t = 7.2 in (TABLE 1)

fa = 3,305.2 / 7.2 x 12 = 38.25 psi Actual Axial Stress

fb = (M/bd2) x (2/kj) Actual Bending Stress

Calculate: np, j, k & 2/jk

Assume Reinforcing # 4 @ 16 “

As = 0.20 in2 x 12 /16 = 0.15 in2 /ft

P = As /bd = 0.15 / 12 x 4.75 = 0.0026

n p = 25.778 x 0.0026 = 0.0678

k = [(np)2 + 2np]1/2 – np

k = [(0.0678)2 + 2 x 0.0678]1/2 – 0.0678 = 0.3067

j = 1 – k/3 = 1 – 0.3053/3 = 0.8978

2 / jk = 2 / 0.8978 x 0.3067 = 7.2637

Actual Bending Stress:

Masonry: fb = (M/bd2) x (2/jk)

fb = (8,088.80 /12 in x 4.752 ) x (2/0.8978 x 0.3067)

fb = 216.47 psi


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Steel: fs = (M/bd2) x (1/jp)

fs = (8,088.80 /12 in x 4.82 ) x (1/0.8982 x 0.0026)

fs = 12,614 psi

Step 4: Calculate Maximum Unity Check for masonry and Steel:

Axial Compression and Flexure for Masonry:

38.25 / 147.41 + 216.47 / 249.75 = 0.259 + 0.867 = 1.126 < 1.33 O.K.

Flexure for Steel:

fs / Fs = 12, 614 / 24,000 = 0.52 < 1.33 O.K.

Therefore Use #4 @ 16” S = 16” t = 10” Bar Size = #4


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Attachment 3 – Masonry Wall Design

Example 1 - In-House Developed Program 10" (250 mm) Load Bearing Masonry Block Wall

Assume Wall is pinned at top and bottom Assume DL and LL moments at mid-height of wall M = 0.5 P e See Example 1 Sketch GIVEN

f'm 1,500 psi Per SAES-M-100 & IBC 2003 Table No. 2105.2.21.2

Fs 24,000 psi Per ACI 530-02 (Grade 60 Steel)

Es 29,000,000 psi

Em = 750 f'm 1,125,000 psi

Vertical Bars #4 @16 Assumed vertical reinforcement t 7.2 inch Equivalent Solid Thickness Per TABLE 1 r 3.04 Radius of Gyration per TABLE 2 d 4.75 inch Depth of rebar -At center see TABLE 3 b 12 inch Assume typical 1 ft section of wall Seismic Zone 0 Assume earthquake zone = 0 Duration Factor 1.33 Due to combining with wind load No Special Inspection INPUT Note: All loads given are at top of wall Wall Height 16.4 ft PDL 2200 # / ft PLL 400 # / ft e (eccentricity) 0 inches MDL 0.00 # / ft Moment at mid-height of wall MLL 0.00 # / ft Moment at mid-height of wall Wind Load 20 psf As 0.15 in2/ft - From TABLE 6 (for #4 @ 16 inch) Wt (B. Wall) 86 psf - From TABLE 1


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CALCULATIONS (at mid-height of wall):

n p np k j 2/jk h/r h/140r 70r/h 25.778 0.0026 0.0678 0.306696 0.8978 7.263702 64.74 0.4624 1.081301

PDL Wall PDL+LL MDL+LL MWL MTOT fa fb fs Fa Fb # / ft # / ft #-ft #-ft/ft #-in/ft psi psi psi psi psi

705.2 3,305.2 0.00 672.4

8,069 38.25 216.4704

12,614.2 147.41 249.75 UNITY CHECK Masonry Steel fa/Fa+ fb/Fb fs / Fs 1.126 < 1.33 O.K. 0.526 <1.33 O.K. CONCLUSION: Use #4 @ 16" (12 mm bars @ 400) Vertical Bars Use #5 mm diameter longitudinal truss bars placed at 400 mm (16-inch) centers (per SAES-M-100)

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