I.ABSTRACT:

11th INTERNATIONAL BRICKlBLOCK MASONRY CONFERENCE TONOJI UNIVERSITY, SHANOHAI, CHINA, 14 - 16 OCTOBER 1997

THE TONGUE AND GROOVE DRY MASONRY

Yiqing Yin1

Masonry as an ancient art needs renovation to adapt some criticai situations like earthquake, ease and economic way of construction. A new tongue and groove biaxial block is introduced trying to solve some problems of conventional masonry. Vertical and horizontal preformed cavities make it easy for utility installation and possible to beco me a post-tensioned structure. Its inborn cracking and energy dissipation features make it suitable for multistory buildings. In strong, rare earthquakes the tongue and groove structure is a safeguard oflive and property. Dry masonry not only means no mortar, but a state of dry execution, an easy way of construction and the trend of civilization. For energy saving, environment protection and continuous development, dry masonry is on the way.

2. INTRODUCTION

Masonry, art or trade of building in stone, universally practiced since ancient times. Among the ancient Egyptians, pyramids or other stonework were generally squared and fitted; no adhesive or mortar was used to join the stones. Ancient examples of this Cyclopean masonry, composed of immense irregular natural stones laid together without mortar, have been found throughout Europe, China and Peru. The Chinese, Greeks and Romans developed masonry techniques that have continued in practice with few changes to the present day.

[Keywords: Dry masonry; Biaxial Block; Loadbearing-Wall; Earthquake Resistant; Post­tensioning.]

I Structural Engineer, Department of Civil Engineering, Nanjing Cement Design and Research Institute, 209 Hanzhong Road, Nanjing 210029, China.

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Concrete, artificial engineering material made from a mixture of Portland cement, water, fine and coarse aggregates, and a small amount of air. It is the most widely used construction material in the world. Concrete is the only major building material that can be delivered to the job si te in a plastic state. This unique quality makes concrete desirable as a building material because it can be molded to virtually any form or shape. Concrete provides a wide latitude in surface textures and colors and can be used to construct a wide variety of structures.

Concrete masonry is block and brick building units molded of concrete and used in ali types of masonry construction. Concrete masonry is used for load-bearing and nonload­bearing walls; piers; partitions; fire walls; backup for walls of brick, stone, and stucco facing materiais; fireproofing over steel structural members; firesafe walls around stairwells, elevators, and other enclosures; retaining walls and garden walls; chimneys and fireplaces; concrete floors; and many other purposes.

About 60 percent of ali concrete masonry units. such as cinder blocks, are made with lightweight aggregates. Processed clays, blast-furnace slag, shales, natural vo1canic aggregates, and cinders are the lightweight aggregates most commonly used. The size of the masonry unit most commonly used for walls, both below and above ground, is 20 by 20 by 40 cm (8 by 8 by 16 in). Masonry units are laid horizontally, and are cored to reduce weight and to provide an insulating air space within the block. New types of concrete masonry. such as split and slump block, are being used as facing in homes, commercial buildings, schools, churches, and municipal facilities. Basic block types are fairly well standardized today. Specific types can usually be supplied for any construction without cutting or fitting. Special molds are available for the production of patterned shadow effects on exterior and interior block walls. It is possible to supply virtually any color or type oftexture.

Block machinery is very well developed, especially in industrialized countries. Developing country like China also has its own machinery works to manufacture qualified concrete block making machines. This kind of machine is based on pressure vibration principie to dense and mold the concrete block. A new . method of making concrete block which use vacuum processing technique as well as pressure vibration to fabricate more strength. high quality concrete blocks is under study.

Block we called is a product of industry. Unlike natural stone, block can easily be cast with tongue and groove we need or for the structure's need. So the dry masonry using tongue and groove block is introduced to structure system. A1though the thought and the technique i~ rei ative new, the application is being used in retaining walls, garden walls and load or nonload bearing walls in low-rising buildings.

With the policy and regulation for encouraging constniction companies to use new type of building materiais, the consumption of blocks growths steadily these years in China. But the part used in 10'a4bearing walls is very limited. What material we now have is ali kinds of block or the kind we want it will be. What technical method we can use is all kinds of successful expience we have inherited. What question we will solve is earthquake resistant loadbearing wall system In multistory housing or commercial

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buildings. And further we will also provide a easy way of construction, to let less skilled people be able to install the new systems and to protect designers, engineers, architects and others from lawsuits. Another problem will be solved is module system. In China today, 1M, 2M and 3M systems are mixed in one building. Ali kinds ofregulations and regional preferences had determined only 1 M system can meet ali the requirements. Thermal property of new type of material is considered by material engineers and architects.

Our designing try to solve some ofthese problems. Figure 1. Tongue and groove block, a universal structural block which we now call it Uniblock or UB. Figure 2 is the family members ofUB block. Figure 3 is an iIIustration space connection.

Fig. 1

r', · r',

~~l Fig. 2

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1.

2. 3. 4.

5. 6. 7.

8.

Face Tongue A TongueB Tongue C Groove A GrooveB Vertical Cavity Horizontal Cavity

Fig.3

3.THE QUALITY CONTROL OF MASONRY

From Fig. 3, each block is finnIy connected by tongue and groove with other six blocks from top, bottom, left and right as one body to resist ali kinds of forces. And non of the blocks can easily fail otf from wall while there is an earthquake. For fitness and ductility, thin metal or plastic plates may be inserted between the blocks. Biaxial block improves ease of utility installation. What is more is to create a possibility using post-tensioning technique in forming a prestressed stitf slab or an earthquake resistant shear wall horizontally as well as vertically.

The quality ofunreinforced masonry consists offour aspects: block, mortar, weather and mason while reinforced masonry also will consider reinforcement and grout.

Blocks can be fabricated in a industrialized workshop and the quality can be very well controlled. Today on an automated production line several people using block machinery can produce 10,000 blocks per day, casting a block or a set ofblocks every few seconds. Both processing and manufacturing is very successful.

Mortar is what we want to diminish fram masonry. The quality control of mortar on si te is not so easy since the amount is not very large at one time and sometimes cement, water, sand and lime are not very carefully praportioned or measured, it is only rely on mason's experience.

Weather is controlled by haven. Freezing day, sunny day, raining day is not a good for construction, it will influence the quality of masonry a lot. While execution in dry state weather condition is not at that important and the construction quality can be reliable.

Mason is the major unstable factor to the quality ofmasonry and is also. the most uneasily

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controlled factor. With the decline in craftsmanship, few mason willing to work on "clear water wall" or without cladding. Dry masonry doesn't need much skill to perform since the construction quality can be directly seen by himself and others through smoothness and neatness. With the I M module system there is no work on cutting and fitting.

Considering ali the aspects which intluence the quality of masonry structure, in the building code, the reliability of masonry is lower but the safety factor is higher than other structure systems. It is because the unstable quality ofmaterials which now is main bricks and the construction quality which is based on mason's workmanship . The way to meet the constructional requirements is to · amplifY the forces or to decrease the allowable stress ofmaterials. So unnecessary spending had gone with wind.

There is an essential distinction between the two kinds of masonry on quality control and inspection. Quality control and inspection of conventional masonry is difficult while dry masonry, unlike ancient Cyclopean masonry, not only means no mortar, but a carefully designed structural system, a state of dry execution, an easy way of construction and a

trend of civilization, can really satisfY many ofthe building structures.

4. EARTHQUAKE RESISTnNCE

Conventional unreinforced block masonry has a number of serious drawbacks for earthquake resistance. It is naturally brittle; it has high mass and hence has high inertial response to earthquakes; the structural period of vibration is short, ductility is low, its construction quality is difficult to control; and relatively high strength in compress and low strength in shear so make it difficult to resist an earthquake in unreinforced masoruy. Reinforced hollow concrete block masonry is so far the best way 'tó ' build multistory structure in seismic areas. But it is costly and the construction is relative not easy to perform. Though some of studies and experiments showed seismic behavior of reinforced masonry structure is reliable, some countries like lapan is very cautious of constructing multistory masonry structure.

Structure buildings at about 2/3 of China needs special measurements for earthquake resistance. In some rural areas where for economic, construction and inspection reasons people seldom do or not do as well as the standards required in the building construction code. So a structure system of unreinforced low-rise masonry building which can resist earthquake is needed.

From earthquake response analysis and the analysis of earthquake damage, we know that the features of a good earthquake resistant structure include: light in weight, well ductility, large damping factor, energy dissipation and appreciate stiffness. So to establish a proper earthquake resistant structure system using available techniques interactively is the major job for every structural engineer.

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4.1 Earthquake Response ofUB Block Dry Masonry

Vibration: Every block in the structure is a small mass that will vibrate individually, quit different to a singledegree or multidegree-of-freedom system. This vibration is one way of absorbing earthquake energy.

Damping: The inbom cracking of dry masonry also inherits the fact of high damping value in traditional masonry structure.

Ductility: The stiffness of dry masonry structure can be as strong as that of traditional masonry structure under static loads, it depends on the leveI of prestressing. In most cases its stiffness is lower than traditional masonry structure and it will be more ductile under a strong earthquake.

Energy Dissipation: Energy isolating and dissipating devices are very popular and efficient for earthquake resistance and many applications have been performed ali over the seismic regions. The friction force is the characteristic of the dry masonry and the force will be very large in the lower stories of a multistory building. Despite of this, the prestressed force by post-tensioning can also provide enough compressive stress when there is vertical ground up acceleration or on top stoly where compressive stress is relative lower.

Dry masonry is more suitable for muItistory buildings. The seismic response is not as strong as a traditional masonry building, because it is more ductile. multidegree-of­freedom system when in vibration is in ali directions, balances most offorces especially in higher mode.

5. POST-TENSIONED DRY MASONRY

One of the greatest problem of conventional concrete masonry is the relative higher compressive strength with lower shear strength. The resuIt is that the shear strength of masonry determines the sections despite the much potential of compressive strength. Dry masonry can be prestressed in the same manner as concrete. Some conventional masonry structures also use this technique and were proved very successful.

Both vertical and horizontal the prestressing forces would result 10 a vertical axial compressive stress that would exceed the flexural tension stress resulting from the lateral force . In this way, while under allowable working forces, the entire masonry section could be considered fully effective in resisting lateral forces, the system remains elastic, and lateral deflections could be calculated base on stiffness values for the gross section.

When in a strong earthquake the structure has inelastic response, the tendon is yielded and the tongues work as safeguard of the structure, the domino reaction (breaking of

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tongues) postpones the force act direct1y to structure, and saves the precious time against the duration of earthquake.

The post-tensioning method we mentioned most1y is low-Ievel prestressing. The simple and cost efficient process make it adequate for ali kinds of site construction. To meet some specific requirement like high retaining walls, water pools, silos, high-level prestressing can also be performed ofthis purpose.

On top story or roof areas where compressive stress is lower there is often cracking in the up comer of walls formed by thermal stress, this is very common in unreinforced masonry. When prestressed force presents here, the cracking and leaking problem can be solved. Concrete masonry is very sensitive of earth subsidence, the smaller in size of UB block and prestressing will also limit the cracking problem.

6. DESIGN AND CONSTRUCTlON OF DRY MASONRY

Because story masses are not concentrated at f100r leveis, diaphragms are not stiff and large eccentricities of lateral force may exist about the center of mass, modes of vibration are much more complex than for conventional multistory steei or concrete buildings, which can be analyzed with lumped-mass stick modes. The lateral-force-resisting system therefore needs to be represented with numerical models that are more extensive than commonly used in a design office. But a standard program can calculate ali these for us, some day with speed and capacity of computer continousely growth, a mo dei of multidegree-of-freedom finite element analysis system will be provided to calculate the whole structure fast and accurately.

Remaining of appropriate compressive stress in walls of multistory buildings is more important. Post-tensioning method will be carried out to let loadbearing elements be prestressed. One of the major failure of masonry structure in an earthquake is the dramatic lose of shear strength when compress stress is low or even negative. In dry

masonry, energy dissipation needs friction and it comes from compression.

With IM module system architect wouldn't have additional works for plan or elevation adjustment . The design work is more Iike an integrated system since facility cables, electric and communication lines, pipelines, the decoration details are in one set of drl!wings. With computer aided and network techniques, it is quite easy of ali department's work in a same group. Also on construction process an integrated job will be done by the same workers, fortunately, it is not a difficult work to do.

More attention shall be paid in the first step of construction that is the accuracy,

foundation, walls, p1ans and elevations should be carefully fitted to each other.

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7. IMPLICATIONS

The forming of a structure system is always in pace with the emerging of a new material. Like concrete and steel, they changed the world very much, formed the reinforced concrete structure system and steel structure system. lt seems a passive way of evolution. The conception design of UB block is a positive way of thinking since we now more freedom of choosing materiais and interactive of using the knowledge of ali subjects. For energy saving and environment protection, concrete block is best form of industrialized production. New technique, new manufacture process and new raw material in use, it will realize the goal of continuous development.

Try it, suppose you have no ideas about masonry, what kind ofmasonry unit you wish to design and what kind of masonry structure system you will establish?

REFERENCES

l. Dowrick, D. 1. ."Earthquake Resistant Design: For Engineers and Architects", Second Edition, John Wiley & Sons. Ltd. Chichester, 1987, pp.361-369.

2. Green, N. B. "Earthquake Resistant Building Design and Construction", Elsevier Science Publishing Co., Inc. , New York, 1987.

3. Curtin W. G., Show G. Beck 1. K., "Design of Reinforced and Prestressed Masonry", Thomas Telford, London, 1988.

4 . Abrams D. P. "Masonry Carries the Load", Civil Engineering, ACSE, 63(2), pp.66-67.

5. Tarricone P., "A Tale of Two Laboratories", Civil Engineering, ACSE, 60(7), pp.50-53 .

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