1 Introduction

reduction in overall construction costs and time, comparedwith other materials. Crosswalls are extensively used inschool classroom blocks where one brick thick walls havebeen spaced at about 7 m centres. In halls of residence, hotelbedroom blocks and similar applications, half brick thickwalls have been used spaced at about 3 m centres. Thesewalls are not only space dividers and the base for acousticbarriers, but also form the structure and completely elimin-ate the need for columns and beams.

One of the reasons for the speed of erection mentioned earlier, is illustrated in Figure 1.1, which demonstrates theessential simplicity of brickwork and blockwork structures.A further reason is to be found in the fact that there is a con-tinuous ‘follow on’ of other trades. Several contractors havesuccessfully used the ‘spiral’ method to speed construction,shown in Figure 1.2, and this is described in some detail inChapter 9 (see Figure 9.29).

Useful and economical though they are for a range of appli-cations, both crosswall and cellular construction demandrepetitive floor plans and are therefore not suited to build-ings where the floor plans vary or where large flexible openspaces are required.

The use of masonry as the major structural material inhouse-building has maintained its market share but the usein multi-storey structures has been eclipsed by the greateruse of steel and concrete frames often clad in materialsother than masonry. This is a pity but has been broughtabout primarily by changes in health and safety regulationsrelating to working practices and the shortage of skilledbricklayers.

It is well known that brickwork forms an attractive cladding and that both brickwork and blockwork aredurable sustainable materials with good base thermal andacoustic insulation and excellent fire resistance. Both can be more economic and faster to build if designed anddetailed by a knowledgeable structural engineer. In theirhighly stressed, slender, modern forms, current masonrystructures have no resemblance to previous thick masonrystructures.

1.1 Present Structural Forms

The two most common forms of multi-storey masonry construction are crosswall and cellular construction (seeFigures 14.13 and 14.37) – which can show as much as 10%

(1) fix starter bars

(2) erect kickershutter

(3) cast kicker

(4) strike kickershutter

(5) fix mainreinforcement

(6) erect mainshutter

(7) erectscaffolding

(8) cast column

(9) strike shutter

(1) erectscaffolding

(2) build wall

(1) stop site workin vicinity of steelerection

(2) fix spliceplates or otherconnections

(3) erect column

(4) plumb andline column

(5) paint column

(6) provide fireprotection

concrete column or wall masonry wall steel column

Figure 1.1 Speed of erection compared with steel and concrete

2 Structural Masonry Designers’ Manual

1.2 Examples of Structural Layout SuitingMasonry

The masonry ‘spine wall’ (see Figure 14.36) can be used foroffice blocks, where precast prestressed concrete floor unitscan span up to 8 m onto the corridor walls or spine. Currentthinking in office layout is that the depth of space from a window should be 6 m maximum for natural daylight tobe enjoyed by the user. Coupled with energy costs for light-ing and air-conditioning costs, this form of layout has itsadvantages. Masonry structures also have a naturally highthermal mass aiding natural ventilation and reducing theneed for air-conditioning.

Large spaces in multi-storey structures can be achievedusing columns of high strength bricks or blocks supportingconcrete floors. Single-storey wide-span structures such assports halls can be achieved by using cavity walls stiffenedwith brick piers, diaphragm walls and fin walls. Each ofthese forms provides the structure, the cladding, the baseinsulation and can be erected by the main contractor usingone trade only.

Pier-stiffened cavity walls are economical up to 5 m inheight but, above that, diaphragm and fin walls are moresuitable. The diaphragm wall (see Figure 13.1) has provedvery satisfactory in a number of sports halls, gymnasia,swimming pools, factories, a church, a theatre, and severalmass retaining walls designed by the authors’ practice.

A diaphragm wall consists of two half-brick leaves separ-ated by a wide cavity stiffened by brick cross-ribs. Thestructural action is of a series of I or box sections. Thecladding function is performed by the outer leaf, the insula-tion by and within the cavity, and the lining by the innerleaf. Many such buildings have been constructed in thenorth-west of England in varying weather conditions. They have suffered no distress and above all require littlemaintenance. Their design was chosen on its economicadvantage.

The fin wall (see Figure 13.41), which acts structurally as aseries of connected T sections, has been found to be highlyefficient for tall single-storey structures, and could well be found useful for multi-storey work – particularly for the column warehouse-type structure. The dramatic visualeffect of fin walls can be pleasing. Fin walls readily lendthemselves to post-tensioning. Both post-tensioned brickfins and diaphragm walls have been built up to 10 m high

and, with the results of diaphragm wall research, it is evid-ent that post-tensioned fins and diaphragms could be builtto an even greater height.

Engineers will probably be interested in the simplicity of diaphragm and fin wall design, contractors will welcomethe elimination of sub-contractors and suppliers, and archi-tects will welcome the wide choice of architectural treat-ments. Clients are likely to be pleased with good-lookingbuildings with lower heating costs, and which are durableand maintenance-free. Some cladding manufacturers pro-udly guarantee their products for a twenty-year life. Masonrycan be guaranteed for a lot longer life and frequently itsappearance improves with age.

1.3 Reinforced and Post-tensioned Masonry

Brickwork and blockwork, like concrete, have high com-pressive strength but relatively low tensile resistance. So, as with concrete, reinforcing and post-tensioning can beused to carry or relieve the tensile stresses. Reinforcedbrickwork has been used in India and Japan since the FirstWorld War and in America since the Second World War. In Britain reinforced and prestressed masonry is also usedby structural engineers for structures such as retainingwalls, tanks and footbridges.

The authors’ practice was one of the earlier pioneers ofpost-tensioned masonry, particularly in low-rise structuressuch as schools and libraries where lateral wind loadingproduces excessive bending moments for traditional plainmasonry. More recently the authors’ practice used a syn-thetic rope ‘Parafil’ as the prestressing tendon in a foot-bridge design.

Current health and safety requirements, which limit theweight of any item that one person can regularly lift manu-ally to 20 kg, have led blockwork manufacturers to producea greater range of dense concrete blocks with voids. Thesevoids can be used to include reinforcing bars for a rein-forced masonry structure.

1.4 Arches and Vaults

Whole life costs, sustainability issues and aesthetics haveled to a renewed interest in older structural forms, particu-larly the arch. Several highway arch bridges have been builtfor spans up to 15 m, producing an aesthetically pleasingform which requires little or no maintenance. The authors’practice was instrumental in the construction of two pre-stressed flat arch pedestrian footbridges at Tring, Herts in1995. The arches were constructed vertically on site, pre-stressed and then lifted into place using a crane. This is agood example of prefabrication (see section 1.6).

1.5 The Robustness of Masonry Structures

Robustness is a requirement that all structural engineersmust consider in their design work. It was previouslyimplied in many structures which had a cellular form andin which elements were automatically tied to each other asa result of construction practice. The partial collapse of a

1. erect slabshutter

2. fix reinforcement

3. castslab

4. erect nextlift of masonry

5. ‘follow on’ tradesstart on floor below

Figure 1.2 Sequence of masonry construction

Introduction 3

block of flats at Ronan Point in 1968 led to a change in PartA of The Building Regulations, which required structuralengineers working on certain buildings to consider dis-proportionate collapse in their design. The requirement ofclients and architects for lighter structures with claddingsystems and open-plan layouts has led to further amend-ments to the The Building Regulations, Part A. The revisedrules specify tying requirements and the building typeswhich must now be designed to meet these rules. Carefuldesign and consideration of these rules should not ad-versely affect the choice of masonry as a structural material.

1.6 Prefabrication

The recent initiatives in the construction industry such as Latham, Egan and the current ‘Best Practice’ initiativehave made construction professionals think more about the whole practice of building procurement rather than justthe specific requirement of each discipline. Construction islooked upon as a manufacturing process rather than an ad hoc process. There is a drive for the use of more pre-fabricated elements produced under factory conditions withgreater quality control. The structural steelwork industryand the precast concrete industry already provide this facility.

The Construction Design and Management (CDM) Regula-tions impose a duty of care upon a structural engineer toconsider the safe construction and maintenance of anydesign proposal. Linking this requirement with the fact thatthe majority of fatalities in the construction industry are asa result of falling from height then the choice of structureought to limit the time any person is working at height.Prefabrication is one way of achieving this. Many multi-storey structures are being clad using prefabricated panelsof many materials such as glass, steel sheeting, pvc panels,to the detriment of masonry, which is a more sustainablematerial. Precast masonry panels have been used on struc-tures in the past but this is reducing with the insulationrequirements specified in Part E of The Building Regula-tions. This is a pity since masonry has an aesthetic qualitywhich improves with age.

1.7 Future Tradesmen

There is currently a deficit of 5% in qualified brick and blocklayers within the industry. This is expected to increase to7% in the short term. Construction’s answer may be to usethe factory produced panels described above.

1.8 Engineering EducationAt the beginning of the Victorian era, bricks were the main civil and structural engineering materials. Sir MarcBrunel used reinforced brick rings for the shafts of theBlackwall Tunnel. His son, Isambard Kingdom Brunel,used brick arches of over 100 ft span to bridge the Thamesat Maidenhead. Stephenson carried out research into thecompressive strength of brickwork when he was designingand building the Conway Bridge. Jesse Hartley madeextensive use of structural brickwork in the construction ofthe superb Albert Dock in Liverpool, and Telford did thesame in the elegant modernised St Katherine’s Dock inLondon. The Victorians used bricks to retain canal and rail-way cutting embankments, for aqueducts, tunnels andsewer linings, deep manholes and inspection chambers,road foundations, bridges, warehouses, cotton mills, fac-tories, railway stations, churches, houses – every conceivabletype of building and engineering structure.

However, the advent of steel and reinforced concrete, withtheir superior tensile and bending strength, marked thedecline of structural brickwork. Engineers adopted the newmaterials with great enthusiasm and, since the end of thenineteenth century, the decrease in the use of structuralbrickwork has been so sharp that few, if any, engineeringgraduates can truely design in the material.

Many university civil engineering courses do not teachstructural masonry as part of structural design studies.However as long as graduates are competent in theirunderstanding of stress, bending theory, slenderness ratio,reinforced and prestressed material theory and other struc-tural engineering principles, along with an awareness of construction details that will affect behaviour such aseffective length of struts, then the detailed design should be learnt in practice. Undergraduate civil engineering programmes are being required to deliver a much broadercurriculum than in the past and as a result few graduatescan immediately design masonry structures. The graduateshowever should be able to produce preliminary designs for a masonry structure, based on structural engineeringprinciples.

Using masonry as a solution to a design problem willrequire the masonry industry from suppliers, structuralengineers and contractors to rethink their approach todesign and construction and to see the many opportunitiesthat structural masonry offers clients, users and the generalpublic.