1fi. l~ehlf~.rce~1 111:ls~"lr\' l-e,'isite~l. tell \'e:lI-s hlfel-.

Walter L. Dickey, Masonry Research, Los Angeles, Califomia

The author presented a paper in 1956 before the Building Research Institute of the National Academy of Sciences in Washington, D. C. entitled "Reinforced Brick Masonry"l. It discussed reinforced brick masonry then in use in California. That article will be summarized briefly and then reviewed herein, particularly to confirm some earlier points and to discuss advances that have been made in this decade.

It will be reviewed especially in the light of improvement of use and of increased earthquake resistance design data.

This latter is important because the discussion of the Long Beach Earthquake in that 1956 article is still valid, namely that unreinforced and unengineered structures may be hazards during earthquakes. One comment made then is that "some of the brick structures that were demolished by the Long Beach Quake were identical to many of the brick structures now being built in the East (since that last big earthquake occurred in that area). The first earthquake for many of those buildings will probably be their last ... " We do not predict a quake soon, but records as shown on seismic charts indicate that quakes have occurred in those areas in the past, and therefore may probably occur again. (See Figure 16-1)

In confirming that we cannot predict occurrence of earthquakes one authority stated, "The only thing we may state for certain is that the farther we are from the last quake the closer we are to the next one." (See Figure 16-1.)

The conclusion of that earlier article of a decade ago is as follows:

We have described the details. advantages, and disadvantages of RBM. AIthough RBM was developed initially in the West to meet a need for an economical earthquake resistant construction , it has certain inherent qualities making it effective in any area. As a consequence it may make the use of masomy feasible and more desirable than some other material in many instances. Furthermore, no area is entirely free from earthquakes, some of the strongest known have occurred in the East. It might, therefore, be well to take advantage of RBM's inherent safety factor.

110

To sum up: RBM is the technique of laying exterior and interior wythes of

masomy with a grout collar joint in which reinforcement is placed. It provides ma~omy surfaces of elements of different heights,

types , and coursing, ali incorporated into a homogeneous structure. It has an adaptability and freedom of expression which could be

more fully realized . Design theory is identical to reinforced concrete design theory. Validity of the principies and theory have been established by

test. It has a tremendous factor of safety over permitted design

values. It is subject to some typical masomy disadvantages, namely,

modular restrictions of size or placement. and sensitivity to human workmanship. It is new and masons must be trained in slightly different techniques.

It has several advantages; for instance : An ageless and warm beauty , with interesting texture and

pattern. A relatively low cost of placement. An elimination of certain human equation factors A low maintenance cost. Excellent resistance to cracking and differential settlement. A finish wall that serves as a structural element. High earthquake resistance. Good atomic blast resistance. Good weather resistance. This discussion will, I hope , help enrich the vocabulary of the

architect and engineer who seeks full . free, uninhibited expression of his creative imagination as well as function . It may also provide food for thought for those who seek economy-better buildings at lower cost.

Purpose

This Chapter pro poses to extend that earlier paper , to examine the validity, to bring it more up to date, and to discuss changes made.

The RBM advantages listed therein are still valid, such as sayjngs in steel reinforcement compared to concrete, savings in structural steel support, economy of reinforcing and laying, improvement of confidence in workmanship, savings due to

Reinforced Masonry Revisited, 10 Years Later 1 I I

I S . Da

9 ~º-_ I ,,_LN e b r

I C o, r'

r li. dO)' K a

I n 8 li. 8

O:....._~_~2&Omll ..

Zone O-No Domage

1- Minor Damage 2 - Moderate Damage 3 - Maj?r Damage

Figure 16-1. Chart indicating where quakes have occurred and are therefore likely to occur again.

the use of reinforced walls, along with the other many aesthetic and intrinsic advantages of brick.

Code Design Revisions

The structural design method for RBM was stated then to be identical with thedesign procedure for reinforced concrete. This is noted to be correct in the ranges of stress permitted by the codes, i.e. with that tremendous facto r of safety. However, reinforced concrete design is becoming more sophisticated and changing in details not applicable to masonry ; therefore, in the newer codes such as the 1967 Uniforrn Building Code, 2 the design provisions were put into the masonry chapter rather than includedmerely by reference to the concrete chapter. AIso, since that time it has been found that a pro per consideration of Es/Em, or "n", and the percentage of steel, that is the "np" value , is influential. This is because the percentage of reinforcement is considerably less than used in concrete, and more economical design can be achieved, i.e. use of less steel for the same facto r of safety. There is economy of design in using proper values of k and j instead of the approximate values.

There have been improvements in methods and techniques , some of which are as follows:

Joint Reinforcing

There has been a wider use and development of joint reinforcing. This is a very convenient economical method of placing reinforcing in masonry walls? There are now examples such as Dur-O-Wall, AA mesh, K mesh, Wallmesh and so forth in the California area.

High Lift Grouting

High lift grouting is an improvement of the method of placing grout in grouted reinforced masonry . It was developed and promoted first in the San Francisco Bay area, then spread to Southern California and to other parts of the country4. This consists essentially of building the brick wythes full height with wire ties between them to serve as form ties , cleaning out the interior, inspecting the steel placement, and then grouting in lifts to the full height of a wall5 . Con­ventional1y such grouting is done in 4' lifts, between vertical barriers which control the flow, and then vibrating for intimate placement. SubsequentIy, after it has partial1y solidi · fied, another 4' height is added, and then another and another until the wall is complete. The grout is generally pumped into place, which makes for economical placing and also assures that the grout will be wet when it is placed. Being wet and

112 Designing, Engineering, and Constructing with Masonry Products

fluid, it develops an intimate bond with the brick . The vibration at time of placing assures a thorough intimate contact and placement around the reinforcing and against the masonry,

In some are as where the brick is highly absorbent, there may be an excessive loss of water and consequent loss of volume. This will permit settlement, segregation or cracking, and bridging or arching. In this case, it is desirable to use an admix to alleviate this situation6 . One aid for placement that has been developed will

1. reduce the amount of water necessary to provide the fluidity,

2. have a water retentive capacity to reduce the water 10ss that might occur,

3. provide an expansion or slight increase in volume during the setting time, so that the mass will remain homogeneous with no shrinkage or separation phenomena at time of setting.

In some areas, with certain brick absorption, it is desirable to vibrate or puddle the grout for reconsolidation just before initial set. This is sometimes done at the time of vibration of the upper lift, that is, the vibrator can penetrate the lift being placed and go into the previously placed lift, reconsolidating it.

This high lift technique adds to the other many advantages. Of most import to the designer is that high lift grouting provides a greater assurance of satisfactory conditions within the wall. Inspection at the time of grouting can assure that the interior is clean, that the steel is clean and in the proper place, and that it is there! Other items that might be missed by observation, such as improper bed joints or head joints or improper mortar will be disclosed when the grout is placed, because the 4' or 5' head of grout as a fluid will "proofload" the wall subjecting it to greater stresses than any design stresses to which it may be subjected later under actualloads. Also this technique is self disciplining. Once a wall fails, due to ornission of ties, improper workmanship, or whatever , it is a costly mess to clean up. One can visualize the tangle of brick, reinforcing, grout, mortar, braces, scaffolding and so forth that rnight resulto It is not likely to happen a second time!

Prism Testing

Prism testing was mentioned in the authors 1956 artic1e, and although this method was in existence at that time it is now more widely accepted. It seems obvious that the best way to determine the actual capacity of a heterogeneous collection of materiaIs under load is actually to test them, rather than to try to predict from a brick or mortar strength grout strength, and steel strength what might be developed. For example, in a specific job one wou1d not know the actual effect of the absorption of the brick wythes on the water cement ratio of the grout collar joint unless he tested a sample of the actual construction.

This principIe was used so little initially that it was almost taken out of the Los Angeles City Code because for the 10 or 15 years that it had been in, there had been no use for it . Even

now, it is in only by reference to Uniform Building Code2. However, with the advent of higher buildings and load-bearing wall construction, it became more important, if for no other reason than to assure the engineer of adequate safety and security. The use of the assured higher strength means more efficiency and consequently more competitive and increased use of masonry. Therefore, there has been an increased use of this technique, and there will soon be addititinal variations and improvements to the method. For example, there is now testing underway to refine the corrections due to height-to­thickness ratio.

This requirement of testing affects the specification of materiaIs in several ways. One is the specification of the material itse1f. This must be a little different from earlier specifications to provide for the higher strengths required. One concern in the specification is the description of the testing method necessary to assure that the design strength is developed in the actual construction. Another item is the definitive stipulation of the purchasing of material because there may be a production period required for manufacturing, curing, testing, and delivering of such items, since they may not be in the usual production schedule nor always in stock. There have been instances in which jobs were delayed because the contractors did not order the material soon enough.

The Uniform Building Code provides that samples of the assemblage may be made and tested. These samples called prisms, are to be fabricated of the same materiaIs, n . .tsonry, grout, mortar , and so forth, and under the same conditions, as they will be installed in the wall. Preferably, they should be laid by the same mason.

According to the present code, they are to be a sample of wall 16" high and 16" wide and of the thickness and type of the wall to be tested. In the code, the basis for the standard is a two to one height-to-thickness ratio. If the samples are made higher or lower than this ratio, they should be corrected to obtain the corrected answer, related to the standard.

These prisms are cured for a 28-day period and tested in compression to determine an f~, which is called the ultimate compressive strength. This is the f~ that is used in the code tables to determine the permitted design stresses. Seven-day resuIts may be used if the relationship to the 28-day strengths have been established. Similar samples are made during the conduct of the job to assure that the materiaIs being incorporated into the project will meet the desired strength. This, obviously, is very similar to the method used in inspection of concrete work where test cylinders are made during the conduct of the job to insure that the strengths are being met.

For specification purposes, one may use the paragraphs as spelIed out in the Uniform Building Code,2 which has proved to be a reasonable wording in usage over several years . portions of the Code are reprinted below. *

1. (c) Determination of Masonry Design Strength. 1. General. The value of "f~" shall be determined by tests of

*Reprinted with permission of International Conference of Building Officials, Pasadena, California.

Reinforced Masonry Revisited, 10 Years Later 113

masonry assemblies in accordance with the provisions of paragraph 2 of this Subsection or shaII be assumed in accordance with the provisions of paragraph 3 of this Subsection.

2. Tests. A. General. When the strength "f~" is to be established by

tests , they shaII be made using prisms built of the same materiaIs, under the same conditions and, insofar as possible , with the same bonding arrangements as for the structure. The moisture content of the units at time of laying, consistency of mortar, and workmanship shall be the same as will be used in the structure. The vaIue of "f~" shall be the average of aII specimens tested but shaII be not more than 125 per cent of the rninimum vaIue determined by test , whichever is less .

Testing shaII inc1ude tests in advance of beginning oper­ations and at least one field test during construction per each five thousand square feet (5000 sq. ft.) of wall but not less than three such tests for any building.

The compressive strength "f~" shall be computed by dividing the ultimate 10ad by the net area of the masonry used in the construction of the prisms. The gross area may be used in the determination of "f~" for solid masonry units as defined in U.B.C. Standard No. 24-1-67.

B. Prisms. For walls, prisms shall be sixteen inches (16") high and sixteen inches (16") longo The thickness and type of construction of the specimen shall be similar to the wall under consideration.

For columns, prisms shall be sixteen inches (16") high and not less than eight inches by eight inches (8" x 8") in plano Cores in hollow masonry shaII not be filled, except for solid fIlled construction.

The symbol "f~" shall be taken as the compressive strength of the specimens multiplied by the following correction factor :

where :

Ratio of "hj d" Correction factor

1.5 .86

2.0 1.00

h height of specimen in inches.

2.5 1.11

3.0 1.20

d = minimum dimension of specimen in inches.

C. Storage of Test Prisms. Test prisms shall be stored for seven days in air, at a temperature of 70 degrees, plus or minus 5°F., in a relative hurnidity exceeding 90 per cent, and then in air at a temperature of 70 degrees, plus or minus five degrees , at a relative humidity of 30 per cent to 50 per cent until tested. Prisms shall be capped and tested in compression similar to tests for molded concrete cylinders as specified in U.B.C. Standard No. 26-10-67.

D. Sampling. Not less than five specimens shaII be made for each initiaI preliminary test to establish "f~." Not less than three shall be made for each field test to confirm that the materiaIs are as assumed in the designo The standard age Df tcsL specimens shall be 28 days, but seven-day tcsts may be used, provided the relation betwecIl the seven-day and 28-day strengths of the masunry is established by adequate test data for the materiaIs used.

LU U)

z o a. U)

LU Q:

1.0

....J 0.5 .. a:: I­u LU a. fJ) .. fJ)

!t;"' 0.25'T ;-S,[ •• x.' 1.00

jJ '--S. '0.30 + 2.80T FOR T'0.25

\ I / \

1 \ ÇD MOOEL RESPONSE SPECTRUM

V "<-S. '0.25/T

~030'S, ........ ............ --I--

1.0 2.0 3.0 T' PE R [00 SECON OS

Figure 16-2. Response spectrum showing response of single mass elements ofvarious periods ofvibration T

Testing

Tests show that masonry has extremely high values in compression and that reasonable tension values can be developed. Also, tests show that masonry does not buckle within the range of wall sizes that may be built. This confirms the indications of the buckling theory of thin plates such as presented by Timoshenko. This indicates, for examp1e, that a wall 3" thick would not be su bject to shear buckling until it is about 16' . Obvious1y, there is a much greater safety factor in bearing walls than in almost any other type of construction. Tests have confirmed this and steps are being taken to correct codes accordingly. The extensive testing is not listed here in detail.

Damping

Damping is an important factor in the response of a building to shaking, such as due to earthquake , and tests have shown that masonry under vibration will develop tremendous damping characteristics12 . How great these characteristics are is not yet well documented, but tests are being made to determine this . The great damping characteristic is probably one of the factors contributing to the excellent performance of masonry in earthquakes9 . (Note Figures 16-2 and 16-3.)

Earthquake Performance of Masonry

To recognize a negative note , masonry has a poor image in many locales because of the poor performance of some unengineered, unreinforced, or unanchored masonry. Some unreinforced structures have shown satisfactory performance e.g. , some of the massive or conservatively built structures.

However, reinforced masonry has performed quite well in even the most severe quakes. For example, 85 percent of the masonry buildings that were reinforced and proper1y tied showed no damage in the major earthquake in Anchorage, Alaska. The difficulty in Anchorage was, not enough anchor-

114 Designing, Engineering, and Constructing with Masonry Products

3.0

2.0

~'" 111 1.0

>1:;= 0.9

~ o.S c 0.7 .'!! <> 0.6

;;:: Qj o 0.5 <> li>

~ 0 .4 .E ~ ~ 0.3 --J

0.2

o. I O

1\

\ \ A ~~L \A ;...,

\ \ I \ \ V \

A. \ /\ ,;, \./ \1 \- No domping

!\. \ i\ \, '/ --1\\ \~ I

\~ ~002 \ ~ \ \ /\ \

-------\ ~;010 "'V' / I'\t~

'---

"" ~

~ ---"'---V -

0.5 1.0 1.5 2.0 2.5

Undamped natural period T, sec.

Figure 16-3. A plot of response to quake against period T for various conditions of damping.

age. This includes major industrial, commercial, and insti­tutional buildings as well as residential.

The author's design experience confirms the satisfactory performance. A series of concrete masonry warehouses was designed by him for Elmendorf Air Force Base near Anchor­age. These were 30' high with wide spacing of reinforcing, 4' and more. These showed no distress whatever, even though subjected to that major quake. It is to be noted that some tilt-up warehouses were built on the site prior to the author's masonry wall designs and were similar in size, i.e., 200' x 1000'. Two segments of the tilt-up buildings collapsed and three were seriously damaged, confirming that the quake was major, or catastrophic, at least to those buildings9. Figure 164 shows the damaged buildings on the site, confirming the quake intensity at the site, and the Figure 16-5 shows the complete lack of damage to the masonry buildings.

The author was pleased to note that two other structures of his design in Alaska were not damaged, the Power Plants at Elmendorf Air Force Base, and at Fort Richardson.

The above factual observations confirm that properly designed reinforced masonry structures perform quite well in resisting quakes, better than might be popularly anticipated.

Research is now being done in order to understand the reasons. There are several probable contributory facts, e.g.:

1. Properly designed buildings perform in a dramatical1y satisfactory manner compared to unanchored, undesigned buildings of Zero factors of safety to lateralloads.

2. The damping characteristics of masonry reduce the response to quakes.

3. The natural frequency of these stiff structures may place them in the short period range where they have less response to quakes, though there is no lessening of the code design requirements. See Figure 16-2.

4. Failures in reinforced masonry are of the ductile type which is a very effective type of resistance to catastrophic quakes. The avoiding of brittle or sudden complete failures is regarded as very important.

Multi-story Bearing Wall Construction

There has been a greater recognition of the tremendous bearing capacity of masonry since there has been greater assurance of earthquake resistance and capacity of such structures when properly engineered. In actual practice, this scheme has turned out to be a surprisingly effective one. It rnight be called a natural use of masonry. There have been very many side benefits derived. The construction is fast, eco· nomical, can be operated on a production line type of operation, and, properly designed, provides extremely high security and factor of safety. (SCPI and NCMA as well as others have developed many publications describing examples and further explaining of the method.) There have been many high rise, or multi-story programs in other countries and some in the U.S.A. Apparent1y, the highest one in the U.S.A. is the Park Mayfair complex in Denver. This is not in a Zone 3 but with slight revisions could have been made to comply.

Earthquake Design Factors and Codes

The Structural Engineers Association of California has been intensely concerned with earthquake design for many years, especial1y because of the relatively great frequency of earth­quakes in the California area. The quakes may not be more severe in California than in other areas, but their frequency is much greater. Therefore building officials and structural engineers are constant1y aware of the subject, perhaps even hypersensitive.

The action of earthquake on a building is not a simple static consideration, although a simplification is to consider static lateral loads assumed applied on the building in the hope that thé assumption can be adjusted in magnitude so that the forces assumed would be comparable to those that would actuaI1y occur in event of a quake.

We might say that the earthquake considerations are divided into two basic types: (1) general considerations of layout, rotation, distribution of masses, actual effect of vibration on the buildings and (2) manipulation of numbers to arrive at a reasonable order of magnitude of the assumed forces to be resisted.

The first facto r , "general considerations," is more the application of judgement, common sense, and experience. Many times slight revisions to the layout of the building can change it from one that might fail due to torsion or disasteroUs distribution of loads and deflections in a quake to one that

would be highly resistant to earthquake.

Reinforced Masonry Revisited, 10 Years Later 115

Perhaps the most important factor to consider in earth­quake resistance is recognition that it is not a static load function but a vibrating load or shaking load that can occur in any direction, east , west , north, south, up , or down. In general, the up and down factors are not considered in earthquake load assumptions because there is already so much facto r of safety for verticalload that additional is not required for the short-time additional load and the slight probability of full design load at time of quake. For certain conditions this must be considered, though, such as for possibility of cantilever projections corning in tune with the random vibration with consequent great response. However, as a result of experience with earthquakes, and study, the "Lateral Force Recommendations" of the Structural Engineers Association 10 has been developed as the best earthquake considerations for major earthquake areas, such as Zone 3 (some of thearbitrary requirements might be deleted for Zones O, 1 ar 2 with their lesser requirements, although the "General Considerations" would be applicable.)

Design

Nomenclature2 (Taken ffOm the Uniform Building Code of the State of California.)

Box System is a structural system without a complete verticalload-<:arrying space frame. In this system the required lateral forces are resisted by shear walls as hereinafter defined.

Shear Wall is a wall designed to resist lateral forces parallel to the wall. Braced frames subjected primarily to axial strcsses shall be considered as shear walls for the purpose of this definition.

(c) Symbols and Notations. The following symbols and notations apply only to the provisions of this Section.

c = Numerical coefficient for base shear as specified in Section 2314 (d) 1.

Cp = Numerical coefficient as specified in Section 2314 (d) 2 and as set forth in Table No. 23-1. (Table 16-1, this Chapter).

D The dimension of the building in feet in a direction parallel to the applied forces.

Ds = The plan dimension of the vertical lateral force resisting system in feet.

Fi,Fn,Fx= Lateral forces applied to a leveI "i," "n," or "x," respectively.

F p Lateral forces on the part of the structure and in the direction under consideration.

Ft = That portion of "V" considered concentrated at the top of the structure, at the leveI "n." The remaining portion of the total base shear "V" shall be distributed over the height of the structure including leveI "n" according to Formula (14-5).

H The height of the main portion of the building in feet above the base.

~,hn ,hx = Height in feet above the base to leveI "i," "n," or "x," respectively.

J Numerical coefficient for base moment as speci­fied in Section 2314 (h) .

Figure 16-4. Tilt-up warehouses at Elmendorf Air Force Base afier Alaskan earthquake.

Figure 16-5. Warehouses at Elmendorf Air Force Base, showing no damage, after the Alaskan earthquake, 200 ft. wide by 1000 ft. longo

K

LeveI i

LeveI n

LeveI x M

V W

Numerical coefficient for overturning moment at leveI "x."

= Numerical coefficient as set Forth in Table No. 23-H.

= LeveI of the structure referred to by the subscript "~o " l.

= That leveI which is uppermost in the main portion of the structure. That leveI which is under design consideration.

= Overturning moment at the base of the building ar structure.

= The overturning moment at leveI "x." = Total number of stories above exterior grade. = Fundamental period of vibration of the building or

structure in seconds in the direction under con­sideration. Total lateral load or shear at the base.

= Total dead load including partitions using the actual weight of the partitions ar the partition loading specified in Section 2302 (b).

116 Designing, Engineering, and Constructing with Masonry Products

n

W = ~Wj

i = 1

Exception: "W" shall be equal to the total dead load plus 25 per cent of the floor live load in storage and warehouse occupancies.

Wj,Wx That portion of "W" which is located at or is assigned to leveI "i" or "x" respectively.

Wp = The weight of a part or portion of a structure. Z Numerical coefficient dependent upon the zone as

deterrnined by the map shown in Figure 16-1. For locations in Zone No. 1 "Z" shall be equal to one-fourth. For locations in Zone No. 2 "Z" shall be equal to one-half. For locations in Zone 3 "Z" shall be equal to one.

Table 16-1 is for selection of the factor Cp in the equation for calculation of forces on various portions of the building, not for determination of load on the building.

(16-1)

The values of "Cp" are set forth in Table 16-1. The distribution of these forces shall be according to the gravity loads pertaining thereto.

(h) Combined axial and flexural stresses. Members subject to combined axial and flexural stresses shall be so propor­tioned that the quantity

where : fa = Computed axial unit stress, determined from total

axialload and effective area. F a = Axial unit stress permitted by this Code at the point

under consideration, if member were carrying axial load only, including any increase in stress allowed by this Section.

fb = Computed flexural unit stress. Fb = Flexural unit stress perrnitted by this Code, if

member were carrying bending load only, including any increase in stress allowed by this Section.

This is not always true nor accurate , but it is used as an acceptable expression that the percent a member is developed in bending plus the percent it is developed in direct stress must not add to more than 100% developed.

Design Synopsis

Occupancy Type of occupancy and use , with the area required will

govern the type of construction, fire rating, etc.

Area Type of Construction Req. Fire Rating, Walls Reg. Fire Rating, Floors Floor Load - L. L.

D.L. These will be based on the above, as defined elsewhere.

Partition Load Partitions are generally fixed so the specific load as applied

may be used in lieu of an "average" floor load. Equipment Load Roof Load - L. L.

D.L. Verto Wall Load Wind Load

As determined by the site , and height , etc. Shape Factor

This will generally be appropriate only in special structures.

Seismic

Zone = 3 i.e. Z = 1.0

This Zone 3 factor of course is 1.0 in California.

K (Table 23-H) Shearwall. 25% Frame. 100% Frame.

K = 1.33 K= .80 K= .67

Once this factor K is determined according to this scheme of framing, that scheme must be followed through- like considering a chain, link after link. The Box system is considered in this text as the most appropriate use of Masonry.

Scheme of Structure

For example: Floor and roof slabs with in tegral finish are 1 way slabs, simply supported for vertical 10ad, and bear on walls. Lateral loads are carried by shear through the slabs to the walls which act as vertical cantilevers from mat footings .

T 0.05hn

= ~D

C 0.05

---lJT

A Table may be provided to simplify this period deter­mination which uses a simple calculation based on dimensiono Other type calculation to determine could be used in lieu of this simplification and may be more conecto

A Table is provided to simplify calculatian af this constant, the facto r of C dependent on period .

T - 4 3 2.5 2.0 1.5 1.0.8.6 .4 .2 C - .0316.0348 .037.040 .0435.050.054.060.068 .086

Reinforced Masonry Revisited, la Years Later

Table 16-1

Horizontal Force Factor "Cp" for Parts or Portions of Buildings or Other Structures

(Table 23-1, Uniform Building Code - reference 2)

Part of Portion of Buildings

Exterior bearing and nonbearing walls , interior bearing walls and partitions, interior nonbearing walls and partitions over ten feet (10') in height, masonry or concrete fences over six feet (6') in height1

Cantilever parapet and other cantilever walls, except retaining walls

Exterior and interior ornarnentations and appendages

When connected to or a part of a building: towers, tanks , towers and tanks plus contents, chimneys, smokestacks, and pent­houses

When resting on the ground, tank plus effective mass of its contents

Floors and roofs acting as diaphragms3

Connections for exterior panels or for elements complying with Section 2314 (k) 5

Connections for prefabricated structural elements other than walls, with force applied at center of gravity of assembly4

Direction of Force

Normal to flat

surfaee

Normal to flat surfaee

Any direetion

Any direction

Any direction

Any direction

Any direetion

Any horizontal direction

Value ofCp

0.20

1.00

1.00

0.202

0.10

0.10

2.00

0.30

1 See also Section 2312 (b) for rninimum load on deflection criteria for interior partitions. 2When "hn/D" of any building is equal to or greater than five to one inerease value by 50 per eent. 3 Floors and roofs acting as diaphragms shall be designed for a minimum value of "Cp" of 10 per cent

applied to loads tributary from that story unless a greater value of "Cp" is required by the basic seismic formula V = ZKCW.

4 The "W p" shall be equal to the total load plus 25 per cent of the floor live load in storage and warehouse occupancies.

The above factors can now be substituted in the basic equation V = ZKCW. This represents the total base shear,' to be distributed up the building according to the forces determined in equation below.

117

(~~) This represents the ratio of height and plan dimension , in

the direction being considered.

This represents the assumed force to be applied to the levei x and may be simply calculated by tabular formo

This represents the assumed portion of the shear to be concentratcd at the top, the so-called "whiplash" effeet.

Overturning Moment

J = 0.5 ~T2

The value of "J" need not be more than 1.00.

118 Designing, Engineering, and Constructing with Masonry Products

This represents the overturning moment coefficient de­pending upon the period of the building. The ca1culation is simplified by tabular listing:

T 40 30 2.5 2.0 1.5 1.0 .8 .6 .4 .2 .1 J .199 .241 .272 .315.382.500.58.70.92 1.46 2.32

n M = J (Fthn + ~ Fjhj)

i = 1 and

n

Mx = J x [F t (hn - ~ + ~ Fj (hj - hx) ]

i = x where:

This represents the overturning moment determined for the base.

The overturning moment Mx at any leveI "x" shall be determined thus. This, and M, can be solved rather simply by a table.

References

1. Dickey, W. L., "Reinforced Brick Masonry," Modern Masonry Publication 446 of the Building Research Insti­tute , National Academy of Sciences, 1956.

2. Uniform Building Code, Vol. 1, International Conference of Building Officials , 1967 Edition.

3. Dickey, W. L., "Joint Reinforcement ," Masonry Industry Magazine, Apri11965.

4. Person, Oscar F., Sahlberg, Manley W., Harrington, Robert W., "High Lift Grouting System," Testing Project 922, September 1959.

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