ADOPTS WITH AMENDMENTS:

International Existing Building Code 2018 (IEBC 2018)

Heads up: There are no amended sections in this chapter.

The purpose of this chapter is to promote public safety and welfare by reducing the risk of death or injury from the effects of earthquakes on existing unreinforced masonry bearing wall buildings.

The provisions of this chapter are intended as minimum standards for structural seismic resistance, and are established primarily to reduce the risk of life loss or injury. Compliance with these provisions will not necessarily prevent loss of life or injury, or prevent earthquake damage to retrofitted buildings.

The provisions of this chapter shall apply to all existing buildings not more than six stories in height above the base of the structure and having not fewer than one unreinforced masonry bearing wall. The elements regulated by this chapter shall be determined in accordance with Table A102.1. Except as provided herein, other structural provisions of the building code shall apply. This chapter does not apply to the alteration of existing electrical, plumbing, mechanical or fire safety systems.

[BS] TABLE A102.1

ELEMENTS REGULATED BY THIS CHAPTER

BUILDING ELEMENTS SD1
≥ 0.067g < 0.133g ≥ 0.133g < 0.20g ≥ 0.20g < 0.30g > 0.30g
Parapets X X X X
Walls, anchorage X X X X
Walls, h/t ratios   X X X
Walls, in-plane shear   X X X
Diaphragmsa     X X
Diaphragms, shear transferb   X X X
Diaphragms, demand-capacity ratiosb     X X
  1. Applies only to buildings designed according to the general procedures of Section A110.
  2. Applies only to buildings designed according to the special procedures of Section A111.
The provisions of this chapter shall not apply to the strengthening of buildings in Risk Category III or IV. Such buildings shall be strengthened to meet the requirements of the International Building Code for new buildings of the same risk category or other such criteria approved by the code official.

For the purpose of this chapter, the applicable definitions in the building code shall also apply.

[BS] BED JOINT.The horizontal layer of mortar on which a masonry unit is laid.

[BS] COLLAR JOINT. The vertical space between adjacent wythes. A collar joint may contain mortar or grout.

[BS] CROSSWALL. A new or existing wall that meets the requirements of Section A111.3. A crosswall is not a shear wall.

[BS] CROSSWALL SHEAR CAPACITY. The unit shear value times the length of the crosswall, vcLc.

[BS] DETAILED BUILDING SYSTEM ELEMENTS.The localized elements and the interconnections of these elements that define the design of the building.

[BS] DIAPHRAGM EDGE. The intersection of the horizontal diaphragm and a shear wall.

[BS] DIAPHRAGM SHEAR CAPACITY. The unit shear value times the depth of the diaphragm, vuD.

[BS] FLEXIBLE DIAPHRAGM. A diaphragm of wood or untopped metal deck construction in which the horizontal deformation along its length is at least two times the average story drift.

HEAD JOINT.The vertical mortar joint placed between masonry units within the wythe.

[BS] NORMAL WALL. A wall perpendicular to the direction of seismic forces.

[BS] OPEN FRONT.An exterior building wall line on one side only without vertical elements of the seismic force-resisting system in one or more stories.

[BS] POINTING. The process of removal of deteriorated mortar from between masonry units and placement of new mortar. Also known as repointing or tuckpointing for purposes of this chapter.

[BS] REPOINTING. See "Pointing."

[BS] RIGID DIAPHRAGM. A diaphragm of concrete construction or concrete-filled metal deck construction.

[BS] TUCKPOINTING. See "Pointing."

[BS] UNREINFORCED MASONRY (URM).Includes burned clay, concrete or sand-lime brick; hollow clay or concrete block; plain concrete; and hollow clay tile. These materials shall comply with the requirements of Section A106 as applicable.

[BS] UNREINFORCED MASONRY BEARING WALL. A URM wall that provides the vertical support for the reaction of floor or roof-framing members for which the total superimposed vertical load exceeds 100 pounds per linear foot (1459 N/m) of wall length.

[BS] UNREINFORCED MASONRY WALL.A masonry wall that relies on the tensile strength of masonry units, mortar and grout in resisting design loads, and in which the area of reinforcement is less than the minimum amounts as defined for reinforced masonry walls.

[BS] YIELD STORY DRIFT. The lateral displacement of one level relative to the level above or below at which yield stress is first developed in a frame member.

For the purpose of this chapter, the following notations supplement the applicable symbols and notations in the building code.

an= Diameter of core multiplied by its length or the area of the side of a square prism.

A= Cross-sectional area of unreinforced masonry pier or wall, square inches (10-6m2).

Ab= Total area of the bed joints above and below the test specimen for each in-place shear test, square inches (10-6m2).

An= Area of net mortared or grouted section of a wall or wall pier.

D= In-plane width dimension of pier, inches (10-3m), or depth of diaphragm, feet (m).

DCR= Demand-capacity ratio specified in Section A111.4.2.

f'm= Lower bound masonry compressive strength.

fsp= Tensile-splitting strength of masonry.

Fwx= Force applied to a wall at level x, pounds (N).

H= Least clear height of opening on either side of a pier, inches (10-3m).

h/t= Height-to-thickness ratio of URM wall. Height, h, is measured between wall anchorage levels and/or slab-on-grade.

L= Span of diaphragm between shear walls, or span between shear wall and open front, feet (m).

Lc= Length of crosswall, feet (m).

Li= Effective diaphragm span for an open-front building specified in Section A111.8, feet (m).

P= Applied force as determined by standard test method of ASTM C496 or ASTM E519, pounds (N).

PD= Superimposed dead load at the location under consideration, pounds (N). For determination of the rocking shear capacity, dead load at the top of the pier under consideration shall be used.

PD+L= Stress resulting from the dead plus actual live load in place at the time of testing, pounds per square inch (kPa).

Ptest= Splitting tensile test load determined by standard test method ASTM C496, pounds (N).

Pw= Weight of wall, pounds (N).

R= Response modification factor for Ordinary plain masonry shear walls in Bearing Wall System from Table 12.2-1 of ASCE 7, where R= 1.5.

SDS= Design spectral acceleration at short period, in g units.

SD1= Design spectral acceleration at 1-second period, in g units.

va= The shear strength of any URM pier, vmA/1.5 pounds (N).

vc= Unit shear strength for a crosswall sheathed with any of the materials given in Table A108.1(1) or A108.1(2), pounds per foot (N/m).

vmL= Shear strength of unreinforced masonry, pounds per square inch (kPa).

Vaa= The shear strength of any URM pier or wall, pounds (N).

Vca= Total shear capacity of crosswalls in the direction of analysis immediately above the diaphragm level being investigated, vcLc, pounds (N).

Vcb= Total shear capacity of crosswalls in the direction of analysis immediately below the diaphragm level being investigated, vcLc, pounds (N).

Vp= Shear force assigned to a pier on the basis of its relative shear rigidity, pounds (N).

Vr= Pier rocking shear capacity of any URM wall or wall pier, pounds (N).

vtest= Load at incipient cracking for each in-place shear test performed in accordance with Section A106.3.3.1, pounds (N).

vtl= Lower bound mortar shear strength, pounds per square inch (kPa).

vto= Mortar shear test values as specified in Section A106.3.3.5, pounds per square inch (kPa).

vu= Unit shear capacity value for a diaphragm sheathed with any of the materials given in Table A108.1(1) or A108.1(2), pounds per foot (N/m).

Vwx= Total shear force resisted by a shear wall at the level under consideration, pounds (N).

W= Total seismic dead load as defined in the building code, pounds (N).

Wd= Total dead load tributary to a diaphragm level, pounds (N).

Ww= Total dead load of a URM wall above the level under consideration or above an open-front building, pounds (N).

Wwx= Dead load of a URM wall assigned to level x halfway above and below the level under consideration, pounds (N).

ΣvuD= Sum of diaphragm shear capacities of both ends of the diaphragm, pounds (N).

ΣΣvuD= For diaphragms coupled with crosswalls, vuD includes the sum of shear capacities of both ends of diaphragms coupled at and above the level under consideration, pounds (N).

ΣWd= Total dead load of all the diaphragms at and above the level under consideration, pounds (N).

The seismic force-resisting system specified in this chapter shall comply with the International Building Code and referenced standards, except as modified herein.
Alterations and repairs required to meet the provisions of this chapter shall comply with applicable structural requirements of the building code unless specifically provided for in this chapter.

The following construction information shall be included in the plans required by this chapter:

  1. Dimensioned floor and roof plans showing existing walls and the size and spacing of floor and roof-framing members and sheathing materials. The plans shall indicate all existing URM walls, and new crosswalls and shear walls, and their materials of construction. The location of these walls and their openings shall be fully dimensioned and drawn to scale on the plans.
  2. Dimensioned URM wall elevations showing openings, piers, wall classes as defined in Section A106.2.3.8, thickness, heights, wall shear test locations, cracks or damaged portions requiring repairs, the general condition of the mortar joints, and if and where pointing is required. Where the exterior face is veneer, the type of veneer, its thickness and its bonding and/or ties to the structural wall masonry shall be noted.
  3. The type of interior wall and ceiling materials, and framing.
  4. The extent and type of existing wall anchorage to floors and roof where used in the design.
  5. The extent and type of parapet corrections that were previously performed, if any.
  6. Repair details, if any, of cracked or damaged unreinforced masonry walls required to resist forces specified in this chapter.
  7. All other plans, sections and details necessary to delineate required retrofit construction.
  8. The design procedure used shall be stated on both the plans and the permit application.
  9. Details of the anchor prequalification program required by Section A107.5.3, if used, including location and results of all tests.
  10. Quality assurance requirements of special inspection for all new construction materials and for retrofit construction including: anchor tests, pointing or repointing of mortar joints, installation of adhesive or mechanical anchors, and other elements as deemed necessary to ensure compliance with this chapter.

Structural observation, in accordance with Section 1704.5 of the International Building Code, shall be required for all structures in which seismic retrofit is being performed in accordance with this chapter. Structural observation shall include visual observation of work for compliance with the approved construction documents and confirmation of existing conditions assumed during design.

Structural testing and inspection for new and existing construction materials shall be in accordance with the building code, except as modified by this chapter.

Special inspection as described in Section A105.3, Item 10, shall be provided equivalent to Level 3 as prescribed in TMS 402, Table 3.1(2).

Existing materials used as part of the required vertical load-carrying or seismic force-resisting system shall be evaluated by on-site investigation and: determined to be in good condition (free of degraded mortar, degraded masonry units or significant cracking); or shall be repaired, enhanced, retrofitted or removed and replaced with new materials. Mortar joint deterioration shall be patched by pointing or repointing of the eroded joint in accordance with Section A106.2.3.9. Existing significant cracks in solid unit unreinforced and solid grouted hollow unit masonry shall be repaired.
Unreinforced masonry walls used to support vertical loads or seismic forces parallel and perpendicular to the wall plane shall be tested as specified in this section. Masonry that does not meet the minimum requirements established by this chapter shall be repaired, enhanced, removed and replaced with new materials, or alternatively, shall have its structural functions replaced with new materials and shall be anchored to supporting elements.
Unreinforced masonry walls shall be laid in a running bond pattern.

The facing and backing wythes of multiple-wythe walls shall be bonded so that not less than 10 percent of the exposed face area is composed of solid headers extending not less than 4 inches (102 mm) into the backing wythes. The clear distance between adjacent header courses shall not exceed 24 inches (610 mm) vertically or horizontally. Where backing consists of two or more wythes, the headers shall extend not less than 4 inches (102 mm) into the most distant wythe, or the backing wythes shall be bonded together with separate headers for which the area and spacing conform to the foregoing. Wythes of walls not meeting these requirements shall be considered to be veneer, and shall not be included in the effective thickness used in calculating the height-to-thickness ratio and the shear capacity strength of the wall.

Exception:Where SD1 is 0.3 g or less, veneer wythes anchored and made composite with backup masonry are permitted to be used for calculation of the effective thickness.

Grouted or ungrouted hollow concrete masonry units shall be tested in accordance with ASTM C140. Grouted or ungrouted structural clay load-bearing tile shall be tested in accordance with ASTM C34.
Lay-up patterns other than those specified in Section A106.2.2.1 are allowed if their performance can be justified.

Mortar shear test values, vto, shall be obtained by one of the following:

  1. ASTM C1531.
  2. For masonry walls that have high shear strength mortar, or where in-place testing is not practical because of crushing or other failure mode of the masonry, alternative procedures for testing shall be used in accordance with Section A106.2.3.2.

The tensile-splitting strength of existing masonry, fsp, or the prism strength of existing masonry, f'm, is permitted to be determined in accordance with ASTM C496 and calculated by the following equation:

(Equation A1-1)
The shear tests shall be taken at locations representative of the mortar conditions throughout the building. Test locations shall be determined at the building site by the registered design professional in charge. Results of all tests and their locations shall be recorded.

The minimum number of tests per masonry class shall be determined as follows:

  1. At each of both the first and top stories, not less than two tests per wall or line of wall elements providing a common line of resistance to seismic forces.
  2. At each of all other stories, not less than one test per wall or line of wall elements providing a common line of resistance to seismic forces.
  3. In any case, not less than one test per 1,500 square feet (139.4 m2) of wall surface and not less than a total of eight tests.
  1. Mortar shear test values, vto, in pounds per square inch (kPa), shall be obtained for each in-place shear test in accordance with the following equation:

    (Equation A1-2)

    where:

    Vtest= Load at first observed movement.

    Ab= Total area of the bed joints above and below the test specimen.

    PD+L= Stress resulting from actual dead plus live loads in place at the time of testing.

  2. Individual unreinforced masonry walls with more than 50 percent of mortar test values, vto, less than 30 pounds per square inch (207 kPa) shall be pointed prior to and retested.
  3. The lower bound mortar shear strength, vtL, is defined as the mean minus one standard deviation of the mortar shear test values, vto.
  4. Unreinforced masonry with mortar shear strength, vtL, less than 30 pounds per square inch (207 kPa) shall be pointed and retested or shall have its structural function replaced, and shall be anchored to supporting elements in accordance with Sections A106.2.1 and A113.8. When existing mortar in any wythe is pointed to increase its shear strength and is retested, the condition of the mortar in the adjacent bed joints of the inner wythe or wythes and the opposite outer wythe shall be examined for extent of deterioration. The shear strength of any wall class shall be not greater than that of the weakest wythe of that class.
  1. The minimum average value of tensile-splitting strength, fsp, as calculated by Equation A1-1 shall be 50 pounds per square inch (344.7 kPa).
  2. Individual unreinforced masonry walls with average tensile-splitting strength of less than 50 pounds per square inch (344.7 kPa) shall be pointed and retested.
  3. The lower-bound mortar strength fspL is defined as the mean minus one standard deviation PD+L of the tensile-splitting test values fsp.
The collar joints shall be inspected at the test locations during each in-place shear test, and estimates of the percentage of surfaces of the adjacent wythe that are covered with mortar shall be reported along with the results of the in-place shear tests.
Existing unreinforced masonry shall be categorized into one or more classes based on shear strength, quality of construction, state of repair, deterioration and weathering. A class shall be characterized by the masonry shear strength determined in accordance with Section A108.2. Classes are defined for whole walls, not for small areas of masonry within a wall. Discretion in the definition of classes of masonry is permitted to avoid unnecessary testing.

Deteriorated mortar joints in unreinforced masonry walls shall be pointed in accordance with the following requirements:

  1. Joint preparation. Deteriorated mortar shall be cut out by means of a toothing chisel or nonimpact power tool until sound mortar is reached, to a depth not less than 3/4 inch (19.1 mm) or twice the thickness of the joint, whichever is less, but not greater than 2 inches (50 mm). Care shall be taken not to damage the masonry edges. After cutting is complete, all loose material shall be removed with a brush, or air or water stream.
  2. Mortar preparation. The mortar mix shall be proportioned as required by the construction specifications and manufacturer's approved instructions.
  3. Packing. The joint into which the mortar is to be packed shall be dampened but without free-standing water. The mortar shall be tightly packed into the joint in layers not exceeding 1/4 inch (6.4 mm) deep until it is filled; then it shall be tooled to a smooth surface to match the original profile.

Nothing shall prevent pointing of any masonry wall joints before testing is performed in accordance with Section A106.2.3, except as required in Section A107.2.

Preparation and mortar pointing shall be performed with special inspection.

Exception:At the discretion of the code official, incidental pointing may be performed without special inspection.

In-place masonry shear tests shall comply with Section A106.2.3.1. Testing of masonry for determination of tensile-splitting strength shall comply with Section A106.2.3.2.
Existing wall anchors used as all or part of the required tension anchors shall be tested in pullout according to Section A107.5.1. Not fewer than four anchors tested per floor shall be tested in pullout, with not fewer than two tests at walls with joists framing into the wall and two tests at walls with joists parallel to the wall, but not less than 10 percent of the total number of existing tension anchors at each level.

New wall anchors embedded in URM walls shall be subject to special inspection prior to placement of the anchor and grout or adhesive in the drilled hole. Five percent of all anchors that do not extend through the wall shall be subject to a direct-tension test, and an additional 20 percent shall be tested using a calibrated torque wrench. Testing shall be performed in accordance with Section A107.5.

New wall anchors embedded in URM walls resisting tension forces or a combination of tension and shear forces shall be subject to special inspection, prior to placement of the anchor and grout or adhesive in the drilled hole. Five percent of all anchors resisting tension forces shall be subject to a direct-tension test, and an additional 20 percent shall be tested using a calibrated torque wrench. Testing shall be performed in accordance with Section A107.5.

Exception:New bolts that extend through the wall with steel plates on the far side of the wall need not be tested.

Tests of anchors in unreinforced masonry walls shall be in accordance with Sections A107.5.1 through A107.5.3. Results of all tests shall be reported to the authority having jurisdiction. The report shall include the test results of maximum load for each test; pass-fail results; corresponding anchor size and type; orientation of loading; details of the anchor installation, testing apparatus and embedment; wall thickness; and joist orientation and proximity to the tested anchor.

The test apparatus shall be supported by the masonry wall. The test procedure for prequalification of tension and shear anchors shall comply with ASTM E488. Existing wall anchors shall be given a preload of 300 pounds (1335 N) before establishing a datum for recording elongation. The tension test load reported shall be recorded at 1/8 inch (3.2 mm) relative movement between the existing anchor and the adjacent masonry surface. New embedded tension anchors shall be subject to a direct tension load of not less than 2.5 times the design load but not less than 1,500 pounds (6672 N) for five minutes.

Exception:Where obstructions occur, the distance between the anchor and the test apparatus support shall be not less than one-half the wall thickness for existing anchors and 75 percent of the embedment length for new embedded anchors.

Anchors embedded in unreinforced masonry walls shall be tested using a torque-calibrated wrench to the following minimum torques:

  • 1/2-inch-diameter (12.7 mm) bolts: 40 foot pounds (54.2 N-m).
  • 5/8-inch-diameter (15.9 mm) bolts: 50 foot pounds (67.8 N-m).
  • 3/4-inch-diameter (19.1 mm) bolts: 60 foot pounds (81.3 N-m).
ASTM E488 or the test procedure in Section A107.5.1 is permitted to be used to determine tension or shear strength values for anchors greater than those permitted by Table A108.1(2). Anchors shall be installed in the same manner and using the same materials as will be used in the actual construction. Not fewer than five tests for each bolt size and type shall be performed for each class of masonry in which they are proposed to be used. The tension and shear strength values for such anchors shall be the lesser of the average ultimate load divided by 5.0 or the average load at which 1/8 inch (3.2 mm) elongation occurs for each size and type of anchor and class of masonry.
  1. Strength values for existing materials are given in Table A108.1(1) and for new materials in Table A108.1(2).
  2. The strength reduction factor, ϕ, shall be taken equal to 1.0.
  3. The use of materials not specified herein shall be based on substantiating research data or engineering judgment, as approved by the code official.

[BS] TABLE A108.1(1)

STRENGTH VALUES FOR EXISTING MATERIALS

EXISTING MATERIALS OR CONFIGURATION OF MATERIALSa STRENGTH VALUES
× 14.594 for N/m
Horizontal diaphragms Roofs with straight sheathing and roofing applied directly to the sheathing. 300 lbs. per ft. for seismic shear
Roofs with diagonal sheathing and roofing applied directly to the sheathing. 750 lbs. per ft. for seismic shear
Floors with straight tongue-and-groove sheathing. 300 lbs. per ft. for seismic shear
Floors with straight sheathing and finished wood flooring with board edges offset or perpendicular. 1,500 lbs. per ft. for seismic shear
Floors with diagonal sheathing and finished wood flooring. 1,800 lbs. per ft. for seismic shear
Metal deck welded with minimal welding.c 1,800 lbs, per ft. for seismic shear
Metal deck welded for seismic resistance.d 3,000 lbs. per ft. for seismic shear
Crosswallsb Plaster on wood or metal lath. 600 lbs. per ft. for seismic shear
Plaster on gypsum lath. 550 lbs. per ft. for seismic shear
Gypsum wallboard, unblocked edges. 200 lbs. per ft. for seismic shear
Gypsum wallboard, blocked edges. 400 lbs. per ft. for seismic shear
Existing footing, wood framing, structural steel, reinforcing steel Plain concrete footings. f'c = 1,500 psi unless otherwise shown by tests
Douglas fir wood. Same as D.F. No. 1
Reinforcing steel. Fy = 40,000 psi maximum
Structural steel. Fy = 33,000 psi maximum

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 pound = 4.4 N, 1 pound per square inch = 6894.75 N/m2, 1 pound per foot = 14.43 N/m.

  1. Material must be sound and in good condition.
  2. Shear values of these materials may be combined, except the total combined value should not exceed 900 pounds per foot.
  3. Minimum 22-gage steel deck with welds to supports satisfying the standards of the Steel Deck Institute.
  4. Minimum 22-gage steel deck with 3/4-inch diameter plug welds at an average spacing not exceeding 8 inches and with sidelap welds appropriate for the deck span.

[BS] TABLE A108.1(2)

STRENGTH VALUES OF NEW MATERIALS USED IN CONJUNCTION WITH EXISTING CONSTRUCTION

NEW MATERIALS OR CONFIGURATION OF MATERIALS STRENGTH VALUES
Horizontal diaphragms Plywood sheathing applied directly over existing straight sheathing with ends of plywood sheets bearing on joists or rafters and edges of plywood located on center of individual sheathing boards. 675 lbs. per ft.
Crosswalls Plywood sheathing applied directly over wood studs; no value should be given to plywood applied over existing plaster or wood sheathing. 1.2 times the value specified in the current building code.
Drywall or plaster applied directly over wood studs. The value specified in the current building code.
Drywall or plaster applied to sheathing over existing wood studs. 50 percent of the value specified in the current building code.
Tension anchorsf Anchors extending entirely through unreinforced masonry wall secured with bearing plates on far side of a wall 30 square inches of area.b,c 5,400 lbs. per anchor for three-wythe minimum walls. 2,700 lbs. for two-wythe walls.
Shear boltse,f Anchors embedded not less than 8 inches into unreinforced masonry walls; anchors should be centered in 21/2-inch-diameter holes with dry-pack or nonshrink grout around the circumference of the anchor. The value for plain masonry specified for solid masonry TMS 402; and no value larger than those given for 3/4-inch bolts should be used.
Combined tension and shear anchorsf Through-anchors—anchors meeting the requirements for shear and for tension anchors.b,c Tension—same as for tension anchors. Shear—same as for shear anchors.
Embedded anchors—anchors extending to the exterior face of the wall with a 21/2-inch round plate under the head and drilled at an angle of 221/2 degrees to the horizontal; installed as specified for shear anchors.a,b,c Tension—3,600 lbs. per anchor. Shear—same as for shear anchors.
Infilled walls Reinforced masonry infilled openings in existing unreinforced masonry walls; provide keys or dowels to match reinforcing. Same as values specified for unreinforced masonry walls.
Reinforced masonryd Masonry piers and walls reinforced per the current building code. The value specified in the current building code for strength design.
Reinforced concreted Concrete footings, walls and piers reinforced as specified in the current building code. The value specified in the current building code for strength design.

For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2, 1 pound = 4.4 N, 1 degree = 0.017 rad, 1 pound per foot = 14.43 N/m, 1 foot = 304.8 mm.

  1. Embedded anchors to be tested as specified in Section A107.4.
  2. Anchors shall be 1/2 inch minimum in diameter.
  3. Drilling for anchors shall be done with an electric rotary drill; impact tools should not be used for drilling holes or tightening anchors and shear bolt nuts.
  4. Load factors or capacity reduction factors shall not be used.
  5. Other bolt sizes, values and installation methods may be used, provided that a testing program is conducted in accordance with Section A107.5.3. The strength value shall be determined by multiplying the calculated allowable value, determined in accordance with Section A107.5.3, by 3.0, and the usable value shall be limited to not greater than 1.5 times the value given in the table. Bolt spacing shall not exceed 6 feet on center and shall be not less than 12 inches on center.
  6. An alternative adhesive anchor bolt system is permitted to be used providing: its properties and installation conform to an ICC Evaluation Service Report; and the report states that the system's use is in unreinforced masonry as an acceptable alternative to Sections A107.4 and A113.1 or TMS 402, Section 2.1.4. The report's allowable values shall be multiplied by a factor of three to obtain strength values and the strength reduction factor, ϕ, shall be taken equal to 1.0.

The unreinforced masonry shear strength, vmL, shall be determined for each masonry class from one of the following equations:

  1. When testing is performed in accordance with Section A106.2.3.1, the unreinforced masonry shear strength, vm, shall be determined by Equation A1-3.

    (Equation A1-3)

    The mortar shear strength values, vtL, shall be determined in accordance with Section A106.2.3.5.

  2. When alternate testing is performed in accordance with Section A106.2.3.2, unreinforced masonry shear, vmL, shall be determined by Equation A1-4.

    (Equation A1-4)
Where any increase in wall dead plus live load compression stress occurs, the maximum compression stress in unreinforced masonry, QG/An, shall not exceed 300 pounds per square inch (2070 kPa).
Unreinforced masonry shall be assumed to have no tensile capacity.
The tension strength of wall anchors shall be the average of the tension test values for anchors having the same wall thickness and framing orientation.
For existing foundations, new total dead loads are permitted to be increased over the existing dead load by 25 percent. New total dead load plus live load plus seismic forces may be increased over the existing dead load plus live load by 50 percent. Higher values may be justified only in conjunction with a geotechnical investigation.
The elements of buildings hereby required to be analyzed are specified in Table A102.1.
Buildings with rigid diaphragms shall be analyzed by the general procedure of Section A110. Buildings with flexible diaphragms shall be analyzed by the general procedure or, where applicable, are permitted to be analyzed by the special procedure of Section A111.

Buildings shall be analyzed to resist minimum lateral forces assumed to act nonconcurrently in the direction of each of the main axes of the structure in accordance with the following:

(Equation A1-5)

Parts and portions of a structure not covered in Section A110.3 shall be analyzed and designed per the current building code, using force levels defined in Section A110.1.

Exceptions:

  1. Unreinforced masonry walls for which height-to-thickness ratios do not exceed ratios set forth inTable A110.2 need not be analyzed for out-of-plane loading. Unreinforced masonry walls that exceed the allowable h/t ratios of Table A110.2 shall be braced according to Section A113.5.
  2. Parapets complying with Section A113.6 need not be analyzed for out-of-plane loading.
  3. Where walls are to be anchored to flexible floor and roof diaphragms, the anchorage shall be in accordance with Section A113.1.

[BS] TABLE A110.2

ALLOWABLE VALUE OF HEIGHT-TO-THICKNESS RATIO OF UNREINFORCED MASONRY WALLS

WALL TYPES 0.13gSD1 < 0.25g 0.25gSD1 < 0.4g SD1 ≥ 0.4g

BUILDINGS WITH CROSSWALLSa
SD1 ≥ 0.4g

ALL OTHER BUILDINGS
Walls of one-story buildings 20 16 16b,c 13
First-story wall of multiple-story building 20 18 16 15
Walls in top story of multiple-story building 14 14 14b,c 9
All other walls 20 16 16 13

For SI: 1 pound per square inch = 6894.75 N/m2

  1. Applies to the special procedures of Section A111 only. See Section A111.7 for other restrictions.
  2. This value of height-to-thickness ratio shall be used where mortar shear tests establish a tested mortar shear strength, vt, of not less than 100 pounds per square inch. This value shall also be used where the tested mortar shear strength is not less than 60 pounds per square inch, and where a visual examination of the collar joint indicates not less than 50-percent mortar coverage.
  3. Where a visual examination of the collar joint indicates not less than 50-percent mortar coverage, and the tested mortar shear strength, vt, is greater than 30 pounds per square inch but less than 60 pounds per square inch, the allowable height-to-thickness ratio may be determined by linear interpolation between the larger and smaller ratios in direct proportion to the tested mortar shear strength.
Vertical seismic force-resisting elements shall be analyzed in accordance with Section A112.
Any redundancy or overstrength factors contained in the building code may be taken as unity. The vertical component of seismic force (Ev) may be taken as zero.

The special procedures of this section shall be applied only to buildings having the following characteristics:

  1. Flexible diaphragms at all levels above the base of the structure.
  2. Vertical elements of the seismic force-resisting system consisting predominantly of masonry or a combination of masonry and concrete shear walls.
  3. Except for single-story buildings with an open front on one side only, not fewer than two lines of vertical elements of the seismic force-resisting system parallel to each axis of the building (see Section A111.8 for open-front buildings).
With the exception of the provisions in Sections A111.4 through A111.7, elements of structures shall comply with Sections A110.2 through A110.4.
Crosswalls shall meet the requirements of this section.

A crosswall is a wood-framed wall sheathed with any of the materials described in Table A108.1(1) or A108.1(2) or other system as defined in Section A111.3.5. Crosswalls shall be spaced not more than 40 feet (12 192 mm) on center measured perpendicular to the direction of consideration, and shall be placed in each story of the building. Crosswalls shall extend the full story height between diaphragms.

Exceptions:

  1. Crosswalls need not be provided at all levels where used in accordance with Section A111.4.2, Item 4.
  2. Existing crosswalls need not be continuous below a wood diaphragm at or within 4 feet (1219 mm) of grade, provided that:

    2.1.   Shear connections and anchorage requirements of Section A111.5 are satisfied at all edges of the diaphragm.

    2.2.   Crosswalls with total shear capacity of 0.5SD1ΣWd interconnect the diaphragm to the foundation.

    2.3.   The demand-capacity ratio of the diaphragm between the crosswalls that are continuous to their foundations does not exceed 2.5, calculated as follows:
    (Equation A1-6)
Within any 40 feet (12 192 mm) measured along the span of the diaphragm, the sum of the crosswall shear capacities shall be not less than 30 percent of the diaphragm shear capacity of the strongest diaphragm at or above the level under consideration.
Existing crosswalls shall have a maximum height-to-length ratio between openings of 1.5 to 1. Existing crosswall connections to diaphragms need not be investigated as long as the crosswall extends to the framing of the diaphragms above and below.
New crosswall connections to the diaphragm shall develop the crosswall shear capacity. New crosswalls shall have the capacity to resist an overturning moment equal to the crosswall shear capacity times the story height. Crosswall overturning moments need not be cumulative over more than two stories.
Other systems, such as moment-resisting frames, may be used as crosswalls provided that the yield story drift does not exceed 1 inch (25 mm) in any story.

A diaphragm is acceptable if the point (L,DCR) on Figure A111.4.1 falls within Region 1, 2 or 3.

For SI: 1 foot = 304.8 mm.

[BS] FIGURE A111.4.1

 ACCEPTABLE DIAPHRAGM SPAN

Demand-capacity ratios shall be calculated for the diaphragm at any level according to the following formulas:

  1. For a diaphragm without qualifying crosswalls at levels immediately above or below:

    (Equation A1-7)
  2. For a diaphragm in a single-story building with qualifying crosswalls, or for a roof diaphragm coupled by crosswalls to the diaphragm directly below:

    (Equation A1-8)
  3. For diaphragms in a multiple-story building with qualifying crosswalls in all levels:

    (Equation A1-9)

    DCR shall be calculated at each level for the set of diaphragms at and above the level under consideration. In addition, the roof diaphragm shall meet the requirements of Equation A1-10.

  4. For a roof diaphragm and the diaphragm directly below, if coupled by crosswalls:

    (Equation A1-10)
An analysis for diaphragm flexure need not be made, and chords need not be provided.
An analysis of diaphragm collector forces shall be made for the transfer of diaphragm edge shears into vertical elements of the lateral force-resisting system. Collector forces may be resisted by new or existing elements.
  1. Diaphragm forces at corners of openings shall be investigated and shall be developed into the diaphragm by new or existing materials.
  2. In addition to the demand-capacity ratios of Section A111.4.2, the demand-capacity ratio of the portion of the diaphragm adjacent to an opening shall be calculated using the opening dimension as the span.
  3. Where an opening occurs in the end quarter of the diaphragm span, the calculation of vuD for the demand-capacity ratio shall be based on the net depth of the diaphragm.

Diaphragms shall be connected to shear walls and new vertical seismic force-resisting elements with connections capable of developing the diaphragm-loading tributary to the shear wall or new seismic force-resisting elements given by the lesser of the following formulas:

(Equation A1-11)

using the Cp values in Table A111.5, or

(Equation A1-12)

[BS] TABLE A111.5

HORIZONTAL FORCE FACTOR, Cp

CONFIGURATION OF MATERIALS Cp
Roofs with straight or diagonal sheathing and roofing applied directly to the sheathing, or floors with straight tongue-and-groove sheathing. 0.50
Diaphragms with double or multiple layers of boards with edges offset, and blocked plywood systems. 0.75
Diaphragms of metal deck without topping:  
  Minimal welding or mechanical attachment. 0.6
  Welded or mechanically attached for seismic resistance. 0.68

The wall story force distributed to a shear wall at any diaphragm level shall be the lesser value calculated as:

(Equation A1-13)

but need not exceed

(Equation A1-14)

The wall story shear shall be the sum of the wall story forces at and above the level of consideration.

(Equation A1-15)
Shear walls shall comply with Section A112.
New seismic force-resisting elements such as moment frames, braced frames or shear walls shall be designed as required by the building code, except that the seismic forces shall be as specified in Section A111.6.1, and the story drift ratio shall be limited to 0.015, except as further limited by Section A112.4.2 for moment frames.

The provisions of Section A110.2 are applicable, except the allowable height-to-thickness ratios given in Table A110.2 shall be determined from Figure A111.4.1 as follows:

  1. In Region 1, height-to-thickness ratios for buildings with crosswalls may be used if qualifying crosswalls are present in all stories.
  2. In Region 2, height-to-thickness ratios for buildings with crosswalls may be used whether or not qualifying crosswalls are present.
  3. In Region 3, height-to-thickness ratios for "all other buildings" shall be used whether or not qualifying crosswalls are present.
Where diaphragms above and below the wall under consideration have demand-capacity ratios in different regions of Figure A11.4.1, the lesser height-to-thickness ratio shall be used.

A single-story building with an open front on one side and crosswalls parallel to the open front may be designed by the following procedure:

  1. Effective diaphragm span, Li, for use in Figure A111.4.1 shall be determined in accordance with the following formula:

    (Equation A1-16)
  2. Diaphragm demand-capacity ratio shall be calculated as:

    (Equation A1-17)
The following requirements are applicable to both the general procedure and the special procedure for analyzing vertical elements of the lateral force-resisting system.
Flexural components of deflection need not be considered in determining the rigidity of an unreinforced masonry wall.

Wall piers shall be analyzed according to the following procedure, which is diagrammed in Figure A112.2.2.

  1. For any pier,

    1.1.   The pier shear capacity shall be calculated as:
    (Equation A1-18)
    where:

    An= area of net mortared or grouted section of a wall or wall pier.

    1.2.   The pier rocking shear capacity shall be calculated as:
    (Equation A1-19)
  2. The wall piers at any level are acceptable if they comply with one of the following modes of behavior:

    2.1.   Rocking controlled mode. Where the pier rocking shear capacity is less than the pier shear capacity, in other words, Vr < va, for each pier in a level, forces in the wall at that level, Vwx, shall be distributed to each pier in proportion to PDD/H.For the wall at that level:
    (Equation A1-20)
    2.2.   Shear controlled mode. Where the pier shear capacity is less than the pier rocking capacity, in other words, va < Vr in one or more pier(s) in a level, forces in the wall at the level, Vwx, shall be distributed to each pier in proportion to D/H.For each pier at that level:
    (Equation A1-21)
    and
    (Equation A1-22)

    If Vp < va for each pier and Vp > Vr for one or more piers, such piers shall be omitted from the analysis, and the procedure shall be repeated for the remaining piers, unless the wall is strengthened and reanalyzed.

  3. Masonry pier tension stress. Unreinforced masonry wall piers need not be analyzed for tension stress.

[BS] FIGURE A112.2.2

 ANALYSIS OF URM WALL IN-PLANE SHEAR FORCES

Shear walls without openings shall be analyzed the same as for walls with openings, except that Vr shall be calculated as follows:

(Equation A1-23)
Plywood-sheathed shear walls may be used to resist lateral forces for URM buildings with flexible diaphragms analyzed according to provisions of Section A111. Plywood-sheathed shear walls shall not be used to share lateral forces with other materials along the same line of resistance.
Seismic forces shall be distributed among the vertical-resisting elements in proportion to their relative rigidities, except that moment-resisting frames shall comply with Section A112.4.2.
Moment-resisting frames shall not be used with an unreinforced masonry wall in a single line of resistance unless the wall has piers that have adequate shear capacity to sustain rocking in accordance with Section A112.2.2. The frames shall be designed in accordance with the building code to resist 100 percent of the seismic forces tributary to that line of resistance, as determined from Section A111.2. The story drift ratio shall be limited to 0.0075.
Unreinforced masonry walls shall be anchored at the roof and floor levels as required in Section A110.2. Ceilings of plaster or similar materials, where not attached directly to roof or floor framing and where abutting masonry walls, shall either be anchored to the walls at a maximum spacing of 6 feet (1829 mm), or be removed.
Anchors shall consist of bolts installed through the wall as specified in Table A108.1(2), or an approved equivalent at a maximum anchor spacing of 6 feet (1829 mm). Wall anchors shall be secured to the framing members parallel or perpendicular to the wall to develop the required forces.
Anchorage of masonry walls to each floor or roof shall resist a minimum force determined as 0.9SDS times the tributary weight or 200 pounds per linear foot (2920 N/m), whichever is greater, acting normal to the wall at the level of the floor or roof. Existing wall anchors, if used, must be tested and meet the requirements of Section A107.5.1 or be upgraded.
At the roof and floor levels, both shear and tension anchors shall be provided within 2 feet (610 mm) horizontally from the inside of the corners of the walls.
Anchors transmitting shear forces shall have a maximum spacing of 6 feet (1829 mm) and shall have nuts installed over malleable iron or plate washers where bearing on wood, and heavy-cut washers where bearing on steel.
Collector elements shall be provided that are capable of transferring the seismic forces originating in other portions of the building to the element providing the resistance to those forces.
Ties and continuity shall conform to the requirements of the building code.
Where a wall height-to-thickness ratio exceeds the specified limits, the wall may be laterally supported by vertical bracing members per Section A113.5.2 or by reducing the wall height by bracing per Section A113.5.3.
Vertical bracing members shall be attached to floor and roof construction for their design loads independently of required wall anchors. Horizontal spacing of vertical bracing members shall not exceed one-half of the unsupported height of the wall or 10 feet (3048 mm). Deflection of such bracing members at design loads shall not exceed one-tenth of the wall thickness.
The wall height may be reduced by bracing elements connected to the floor or roof. Horizontal spacing of the bracing elements and wall anchors shall be as required by design, but shall not exceed 6 feet (1829 mm) on center. Bracing elements shall be detailed to minimize the horizontal displacement of the wall by the vertical displacement of the floor or roof.

Parapets and exterior wall appendages not conforming to this chapter shall be removed, or stabilized or braced to ensure that the parapets and appendages remain in their original positions.

The maximum height of an unbraced unreinforced masonry parapet above the lower of either the level of tension anchors or the roof sheathing shall not exceed the height-to-thickness ratio shown in Table A113.6. If the required parapet height exceeds this maximum height, a bracing system designed for the forces determined in accordance with the building code shall support the top of the parapet. Parapet corrective work must be performed in conjunction with the installation of tension roof anchors.

The height of a URM parapet above any wall anchor shall be not less than 12 inches (305 mm).

Exception: If a reinforced concrete beam is provided at the top of the wall, the height above the wall anchor is permitted to be not less than 6 inches (152 mm).

[BS] TABLE A113.6

MAXIMUM ALLOWABLE HEIGHT-TO-THICKNESS RATIO FOR PARAPETS

  SD1
0.13gSD1 < 0.25g 0.25gSD1 < 0.4g SD1 ≥ 0.4g
Maximum allowable height-to-thickness ratios 2.5 2.5 1.5
  1. Veneer shall be anchored with approved anchor ties conforming to the required design capacity specified in the building code and shall be placed at a maximum spacing of 24 inches (610 mm) with a maximum supported area of 4 square feet (0.372 m2).

    Exception: Existing anchor ties for attaching brick veneer to brick backing shall be acceptable, provided that the ties are in good condition and conform to the following minimum size and material requirements.

        Existing veneer anchor ties shall be considered adequate if they are of corrugated galvanized iron strips not less than 1 inch (25 mm) in width, 8 inches (203 mm) in length and 1/16 inch (1.6 mm) in thickness, or the equivalent.

  2. The location and condition of existing veneer anchor ties shall be verified as follows:

    2.1.   An approved testing laboratory shall verify the location and spacing of the ties and shall submit a report to the code official for approval as part of the structural analysis.

    2.2.   The veneer in a selected area shall be removed to expose a representative sample of ties (not less than four) for inspection by the code official.

Unreinforced masonry walls that do not carry design vertical or lateral loads and that are not required by the design to be part of the lateral force-resisting system shall be adequately anchored to new or existing supporting elements. The anchors and elements shall be designed for the out-of-plane forces specified in the building code. The height- or length-to-thickness ratio between such supporting elements for such walls shall not exceed nine.

Where trusses and beams other than rafters or joists are supported on masonry, independent secondary columns shall be installed to support vertical loads of the roof or floor members.

Exception: Secondary supports are not required where SD1 is less than 0.3 g.

Where elements of adjacent buildings do not have a separation of 5 inches (127 mm) or greater, the allowable height-to-thickness ratios for "all other buildings" per Table A110.2 shall be used in the direction of consideration.

Walls of unburned clay, adobe or stone masonry construction shall conform to the following:

  1. Walls of unburned clay, adobe or stone masonry shall not exceed a height- or length-to-thickness ratio specified in Table A114.1.
  2. Adobe shall be allowed a maximum value of 9 pounds per square inch (62.1 kPa) for shear unless higher values are justified by test.
  3. Mortar for repointing may be of the same soil composition and stabilization as the brick, in lieu of cement mortar.

[BS] TABLE A114.1

MAXIMUM HEIGHT-TO-THICKNESS RATIO FOR ADOBE OR STONE WALLS

  SD1
0.13gSD1 < 0.25g 0.25gSD1 < 0.4g SD1 ≥ 0.4g
One-story buildings 12 10 8
Two-story buildings      
  First story 14 11 9
  Second story 12 10 8
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