1519

GUIDELINES TO CONSTRUCTION METHODS OF REINFORCED MASONRY BUILDINGS

Akio Baba*l,_Katsuro Kamimura*2, Akira Matsumura*3 Yasukazu Takahashi~4, Mitsuyoshi Watanabe~5 , and Osamu Senbu*6

':' lHead '~4'd ':'6Researcher, Di v. of Consto Tech ., Prod uc tion Dept. Head, Div. of Organ ic MateriaIs, Material Dept

Building Research Institute , Ministry of Construction Tateharª 1, Tsukuba-shi, I baraki-ken, #305 JAPAN

~2pro fessor, Utsunomiya University I§hii-machi, 2753, Utsunomiya-shi, #321,JAPAN ~3Associate Professor, Kanagawa University

_ Rokkakubashi 3-27-1, Kanagawa-ku, Yokohama-shi, #221 JAPAN ~4Lecturer , Institute of Vocational Training, Ministry of Labour

Aihara 1960, Sagamihara-shi , Kanagawa-ken , #229 , JAPA N

ABSTRACT

This paper is prepared to introduce the basic concept of the guidelines for reinforced masonry buildings and its actual adoptation to materiaIs and cons tructions of reinforced masonry buildings in Japan, which has been studied and developed under the coordinated research between the Uni ted States and Japan.

Evaluation methods of strength and other properties of grouted masonry , and construction procedures required to reinforced masonry buildings ar e explained herein in order to real ize high reliability in strength , efficiency in construction and durabil ity of this type of structures.

INTRODUCTION

Reinforced masonry is said to be one of the most important types of building structures. Many studies have been done in order to evaluate the structural requirements as structural materiaIs and to realize the reliability in construction proccedures [1, 2, 3 and others].

On the other hand, various kinds of materiaIs and structural methods have been and are actually performed, so it is generally difficult to evaluate the performance and quality of alI types of masonry s tructures. In Japan, masonry structures are not so popular that technological knowledges have

1520

not been compiled since the great damages in unrein force d masonry structures by the Ka nto Earthquake.

RecentIy, the merits of masonr y structures such as high durabiIity and rich appearance, have been being recogized in Japan. A type of reinforced masonry structures has been deveIoped for medium rise buiIdings under the coordinated research between the United States and Japan. A series of r ecomendations for materiaIs and constructions of the type of reinforced masonry structures have been ma de and discussed in a committee unde r the coor dinated program, "BuiIding Construction Committee on Masonry", called BLDCMAR, chaired by an au t hor(KK).

In the guidel ines , the following items are presented.

(1) Requirements to component materiaIs, masonry units, joint mortar and grout

(2 ) Fundamental grade of quality control (3) Test procedures and predic tive methods of prism strength and other

mechanical properties (4) Durability and thickness of cover (5) Construction methods (6) Detecting methods of construct ional defects and repair methods

FUNDAMENTALS OF RECOMMENDATIONS

The contents of the guidelines, at present, are provisionally shown as the follows.

Table of contents

1. General 2. Control of prism strength 3. MateriaIs 4 . Mix proportions and mixing methods of mortar and concrete 5 . Thickness of cover 6. General methods for construction 7 . Laying masonry units 8. Formworks 9. Size and shape of reinforcements and their arrangement

10. Grouting 11. Tests and inspections

In the guidelines, the following item s are especially considered.

(1) Realization of highly leveled ductility and durabil ity (2) Standardization of test methods on reinforced masonry (3) Establishment of predictive methods of prism strength based on the

mechanical properties of the component materiaIs (4) Establishment of estimating methods of the effect of face shells from

the viewpoint of durability (5) Construction systems developed newIy for improving both reliablity and

speed (6) DeveIopments of methods for detecting defects such as faults in grout

1521

REQUIREMENTS TO COMPONENT MATERIALS

Masonry Units General Reguirements Masonry uni ts for reinforced masonry buildings in the guidelines are restricted concerni ng the following items.

(l) Properties of ma terials; compressi ve strength , \"a ter absorp tion rate, permeability of water and depth of water penetration

(2) Shape an d size of units; outer shape, type of horizontal section , ratio of hollow to the whole volume of units, thickness of face shells and height and total thickness of webs

The items are written in the quality standards of units for reinforced masonry buildings which is attached to the guidelines.

Properties .2i Masonry Units : Compressive strength of masonry units is not only one of the most important properties for controlling the quality , but also for estimatin g prism strength as the basic strength of masonry structures .

In the recommendations, both units and grout are effectuated as the strength of structures, so the net stre ngth of units is adopted as the scale of compressive strength which is supposed to be directly related to the durability . The grade of units is classified by the compressive streng th as s hown in Table 1.

Table 1 Grade of Masonry Units

Minimum Strength(kgf/cm2) Grade

Concrete Units Clay Units

1 400 600 2 300 500 3 200 400

The m1n1mum grade of units has a physical meaning which is the lowest val ue to r ealize app r opriate mechanical properties for structural materiaIs especia l ly focusing criticaI stress under uniaxial compression[6).

Shape and Size .2i Masonry Units : The shape of units ap plicable to medium rise building structu r es shall be restric t ed from the various points of view as the follows .

(1) Suf fi cient space in hollow of units for arranging vertical and horizontal rein fo rcements required for the structural performance

(2) Sufficient space for high lift and solidar y grouting (3) Sufficient thickness of webs for avoiding any splitting out of plane

of walls under severe uniaxial loading (4) Appropriate ratio of hollow to solid in units to effectuate both uni t

strength and grout one

1522

Table 2 presents the restriction in the shape of units quantitatively.

Table 2 Rest r ictions on Shape of Uni ts

HolloH Minimum Th ickness ~laximum Ratio Mi nimum Ra tio of Ratio of Face Shells of He ight hleb _,_ Total Thickness

(%) mm to Un it He ight'" of \veb§ to Unit Leng th'"

45-65 25 0.65 0.15

(Note) * Modular Size

The size of units , in length , heig ht an d thickness is standardized in th e provisional re~ommendations on the folloHi ng point s of vi e H,

(1) Systemized bonding methods based on a modular coordination t heory (2) Utilizing modular size in three dimensions (3) Modularizing the spacing of reinforcing bar s horizontally and

ver ti cally (4) Utilizing open end units to deminish Hater leakage i n vertical joi nts

The first and second it ems are alHays required i n masonry buildings . However, the im portance of these items has not alHays been r econginiged in Japan. The thi r d and fo rt h items hav e been neH l y developed i n the proces s of the joint study thr ough compiled discussions in the committee ment ione d pr eviously. The combined bases of module , open end un it s and standardized a r rangement of reinforcements seeme d to be di ff i cu l t to unify in one const ruct ion system.

Firstly, three types of modular systems are recommended as the foll oH s .

( 1 ) 12 Units System (2) 23 Units System (3) Combined Units System Hith 11 and 12 Units

12 , 23 and 11 mean the modular ratio of thickness to length in units Hith open ends.

Secondly , standardization for spacing rei nforc emen ts is r ecommended in Figure 1 as an example Hith a certain thickness .

1523

Figure 1 Examples of Bonding in Horizontal Sec tions

Finally, sta ndard units are presented to correspond the three modular systems respectively as shown in Figure 2.

12 Units 23 Units C Units

Figure 2 Standard Units

1524

Joint MateriaIs Joint materiaIs are genera11y recommended to be ordinary cement mortar without any admixture, because this joint material is very avai1ab1e in Japan and strength of joint can be obtained stab1y. The vo1umetric ratio of sand to cement of 2.5 and 3 is recommended as the standard mix proportion. The mix proportions of mortar can a1ways realize high strength, wh ich is not on1y much effective in stabiIizing prism strength, but a1so comparative1y stable in durability.

Admixtured cement mortar also can be used as joint materiaIs. In the case of using admixtures, prism strength with the admixtured mortar or compressive strength of joint mortar with the admixtures have to be tested in every case.

The required value of compressive strength is dependent on the follow ing items.

(1) Grade of controlling prism strength which depends on the size of buildings and the basic strength of prism characterized in structural designs

(2) Grade of masonry units and kind of materiaIs for units

The detailed prescriptions of controlling prism strength are presented in the third chapter of this paper.

Grout MateriaIs Grout materiaIs are cement mortar or concrete, which are prescribed concerning the following items.

(1) Compressive strength re1ated to required prism strength (2) Slump and maximum size of aggregates required for good compactibility (3) Usage of admixtures for avoiding various kinds of defects in grouting

related to the water abso rption ratio of units and the condition of prewetting

The compressive strength of grout is supposed to be effectuated for realizing necessary prism strength in the guidelines. The necessary strength of grout is presented in the third chapter of this paper.

The maximum size of aggregates is restricted on the basis of the effective size of hol10w in units and the minimum spacing between the inner surface of face shells and adjacent steel bars.

The slump of grout is recommended to be an appropriate value to make the grouting process easy and to be as small as possible. In the case of more than 21 in slump, admixtures shall be used which are super plastisizers or a special kind of admixtures for grout[7].

Admixtures are also recomended to be used in the case of absorptive units as shown in TabIe 4

1525

Table 4 Requirements of Using Admixtures

Units Type of Grout Haterials

Kind of Grade Coarse Fine Haterials

Prewet ting' No-prewetting Prewetting No-prewetting

Concrete 1 (1) (1) (1) (1) 2 (1) (1) (1) 1 3 (1) 1 1 1

Clay 1 (1) 1 (1) 1 2 1 2 1 2 3 2 NA 2 NA

(Note) 1) In case Df ( ) groll t can be llsed without admixture 2) NA means no application

The actual requirements depend on the grade of units, the kind of materiaIs, and the condition of prewetting.

GRADE OF CONTROLLING PRISM STRENGTH

Classification of Quality Control on Site Prism strength is the basic strength for the structural design of masonry structures. Tests on compressive strength shall be performed to control the strength of materiaIs on site. Load bearing capacity of prisms is always so great that the tests sometimes would be impossible. Therefore , the following grades are recommended for the quality control of prism strength.

(1) First grade: Direct control by testing prisms (2) Second grade: Indirect control by a predictive method for prism

strength based on component strength (3) Third grade: Simplified control using the data by producers of units

and grout

What grade shall be selected is dependent on the following items (Refer to Table 5).

(1) Size of buildings (2) Structural design strength of prism

1526

Table 5 Standard Application of Grade for Quality Control

Designed Size of Buildings Prism Strength 3 storied 4 storied 4 storied (kgf/cm2) an~ and and

300m (total 300m2(total 1000m2(total floor area) floor area) floor area)

or 1000m2(total

floor area)

180 3 2 2 210 3 2 2 240 2 2 1 270 1 1 1

First Grade In the case of the first grade quality control of materiaIs strength, prism strength must be tested directly. Sampling method of prisms is specified as the follows,

(1) (2)

(3)

Three specimens shall be taken for one floor. Each specimen shall be made in an appropriate inter vaI to present averaged property of alI the walls of the floor

In the case of more than 400m 2 in the area of the floor, specimen shall be added per 200m 2 of exceeding area in the floor.

The criteria of testing prisms are made as the follows,

the

one

(1) Each experimental value shall not be less than 85% of the designed prism strength.

(2) Averaged value shall not be less than the designed prism strength.

Second Grade Prism strength must be controlled by testing the compress ive strength of grout on site, where the quality of units is controlled and tested in the factory and the quality of joint materiaIs is desired to be tested.

Prism strength can be estimated on the basis of the following equation from the compressive strength of the three component materials[4].

Fcm = es((1-B)fcu+B~fcg}

where, Fcm: Prism Strength fcu: Nominal Unit Strength fcg: Nominal Grout Strength

- - - - - Eq(l)

e s : Constant Determined by Combination of Units and Joints 1:): Volumetric Ratio of Hollow of Units

1527

es is usually ado pted as the value of 0.75, when all the grades of concrete units and the third gr ade of clay unit s are used with normal cement mortar joint specified in mix proportions. In the two following cases, e shall be calculated on the basis of Equation 2 (5 ). s

(1) Us ing t he first and second gr ade clay units (2) Using admixtured cement morta r

ó= fcj/fcu~0.75 o ~ 0 . 75

- - - - - Eq(2)

where , fcj=Nominal Strength of Joint Mortar (Averaged experimental value minus 45kgf/cm2)

In order to select t he component materials, the above equation can be applicable at designing stage. Furthermore, required value of grout strength can be evaluated on the foll owing equation , after units and joints were selected ,

Fcm 1- 8' fcg ~ -- - fcu - - - - - Eq(3)

e 'f': p./ s . Tests for controlllng grout mater i als on site can take one of the following two ways.

(1) Usual test methods using steel cylinders (2) Core test methods drilled from pri s m specimens

Sampling the spec i mens and its diagn osis are the same to the case of the first grade .

Third Grade The thi r d grade of quality control can be applied to comparatively small sca le buildings with low designed prism strength. Factory made ma terials are principally used as units and grout in this t ype of str uctures, so t he most sim plified method can be applicable to this grade of quality control , of which tests in factories must be performed for units and grout .

Table 6 presents the restrictions in this grade .

Table 6 Possible Combination of Component Materials i n Third Grade

Designed Grade of Mix Proportions. Nominal Prism Units of J oint Mortar Stren~*h of Strengt h C : S Grout (kgf/cm2) (by Volume) (kgf/cm2)

180 All 1 : 3 180

21 0 1st or 2nd Grade 1 : 2 . 5 210 Concre t e Units All Clay Uni ts

1528

THICKNESS OF COVER

General Requirement s Reinforced masonry structures are composed of reinforced masenry and reinforced concrete. Thickness of cover shall be kept more than the values sho wn in Table 7 for RM and RC parto

Table 7 Required ~linimum Thickness of Co ver

Compone nts in Buildings Thickness of Cover(mm)

Free from Roof and Indoor 20 Soil Floor Slabs,

Non-Structural Outdoor 30 Walls

Structural Indeer 30 Walls and Beams Outdoor 40':<

Contact to Structural Seil Walls and 1.0

Beams , FIoor Slabs

Foundations 50

(Note) ~ In the case of using effective surface finishing layers, 30mm can be adopted .

Thickness of caver shall be limited to 1.25 times of maximum aggregate size of grout and 10m m for improving compactibility of grout.

Calculation Df Effective Thickness Face shells in reinforced masonry , to a certain ex tent , can be effectua ted as thickness of cove r. Effective thickness of face shells can be caIculated on the basis of the following equations.

In the case of concre t e unit s In the case of clay units

fcu fc u De x Dfo x -- -- Eq(4) De x Dfo x -- - Eq(5)

210 2 210 3

where, De: Effective Thickness (mm) Dfo: Thickness of Face shells (mm) fcu : Nominal Strength of Unit s (kgf/cm2 )

In the above equa tions, ~rout strength and concrete strength in RC part a re supposed to be 210kgf/cm as the desi gned va lue. Two and third mean safety factors for concrete and clay uni ts respectively. The 'difference in the safety factor is depended on different behaviour in carbonation process through the both types of units.

1529

CONSTRUGTION METHODS

General Requirements Construction methods for reinforced masonry buildings are required to be improved in efficiency of construction speed and reliability of cons truction procedures. The following processes are improved in comparison with conventional construction methods in Japan.

(1) Laying Units (2) Bonding Patterns (3) Arrangements of Reinforcements (4) Grouting Methods

Laying Units and Bonding Patterns One of the most elaborate processes is laying units. High lift grouting is specified to an ordinary method, so the process of laying units is restrained in the following items.

(1) Completely Full Bedding (2) Laying height in a day not more than 1 .6m (3) Keeping grout cores clear before grouting

Standard shape units shall be openly ended. Therefore, appropriate bonding patterns are actually limited to the three types as mentioned previously.

Arrangements of Reinforcements Spacings of reinforcements shall be able to be uniform based on modular cordinated layout. Thickness of cover shall be confirmed to be more than the minmum value specified in Table 8. Reinforcements shall be fixed to their appropriate positions in masonry walls, even when the grouting process is performed with vibration.

In order to realize these requirements on site, various conc rete site techniques have been developed while making the guidelines.

Grouting Methods This is the most important process of reinforced masonry constructions which actually determines various performance of masonry walls. The following items are specified from the viewpoints of efficiency in construction speed and reliability in quality.

( 1) High lift grouting (2) Full grouting (3) Cleaning up grouting cores (4) Prewetting corresponded properly to kinds of units (5) Slump and usage of special admixtures for RM grout

DETECTING METHODS OF DEFECTS

In order to improve the reliability of reinforced masonry constructions, many efforts have been done under the cooperative project to develop the non-destructive methods for detecting defects especially focusing on grouting parto

1530

The methods for detecting defects through face shells are classified into the two followings.

(1) To detect defects in grout under grouting procedure (2) To detect defects in grout and between grout and face shells after

grouting

On the first item, further compactive actions are needed just after detecting defects. On the second item, appropriate repair methods shall be adopted as a countermeasure.

Ultrasonic method, analyzing frequency of sound by tapping, ultrared rays and electromagnetic waves have been being examining for detec ting defects in grouting parto At the present, the former two methods are specified in the guidelines.

CONCLUDING REMARKS

Many aspects from the viewpoints of materiaIs and construction procedures are specified in the guidelines. Most of them have been studied and examined under the coopera tive projec t. Some aspects are still tentative specifications and under developing.

The authors hope that the guidelines will be improved through the discussion in the Eighth Brick and Block Masonry Conference.

REFERENCES

M.J.N.Priestley, "P rediction of Masonry Compression Strength," Ne\" Zeal and Concrete Construction, March and April, 1984

2 A.Baba and O.Senbu, "Influencing Factors on Prism Strength of Grouted Grouted Masonry and Fracture Mechanism under Uniaxial Loading," First Joint Technical Coordinating Committee on Masonry Research, Tokyo, Japan, August, 1985

3 G.R.Kingsley and R.H.Atkinson, "A Study on Compressive Stress- Strain Strain Behavior of Concrete and Clay Masonry," ditto

4 A.Baba and O.Senbu, "A Predictive Method of Prism Strength of Grouted Masonr y," Second JTCCMAR, Keystone, USA, Septem ber, 1986

5 A.Baba,'~ Proposal for Prediction of Uniaxial Compressive St~ength of Ungrouted Masonry," BRI Research Paper No. 115, May, 1985

6 A.Baba, O.Senbu, M.Watanabe and Y.Matsushima, "Mechanical Properties of Masonry Units and Test Methods for Determining Compressive Strength," BRI Research Paper No. 118, December, 1985

7 O.Senbu, A.Baba, M.Abe, F.Tomosawa and Y.Matsushima, "Effect of Admixtures on Compactibility and Properties of Grout," Second JTCCMAR, Keystone, USA, September, 1986

8 A.I.J., Japanese Architectural Standard Specifications 7 (JASS 7), Masonry lIlorks