Lets look at the range of tools needed for basic bricklaying. You will recognise some of these from Chapter 3. We can split the tools into three main groups. Tools for: Laying and finishing. To build any wall you will need a trowel to lay the bricks, a pointing trowel and a jointer to provide a finish to the joints. Trowel Pointing trowel Jointer Checking. A spirit level is needed to make sure the work is level and plumb, a set of line and pins to align the bricks accurately and a tape measure to set out and check dimensions. Spirit level Line and pins Tape measure Cutting. To cut the bricks you will need a club (or lump) hammer Scutch hammer and a brick bolster. There are additional tools to cut bricks for A bricklayers hammer with interchangeable different purposes such as a brick hammer and a scutch hammer finishing heads for trimming and tidying bricks and blocks (sometimes called a comb hammer). Club hammer Brick bolster Brick hammer Scutch hammer The correct way to use all of these tools will be discussed later.

Welding of structural steels is governed by the American Welding Society Structural Welding Code, AWS D1.1, the American Institute of Steel Construction Specification for the Design, Fabrication and Erection of Structural Steel for Buildings, or a local building code. AWS D1.1 specifies tests to be used in qualifying welders and types of welds. The AISC Specification and many building codes require, in general, that only qualified welds be used and that they be made only by qualified welders. Structural steels may be welded by shielded metal arc, submerged arc, gas metal arc, flux-cored arc, electroslag, electrogas, or stud-welding processes. Shielded-metal-arc welding fuses parts to be joined by the heat of an electric arc struck between a coated metal electrode and the material being joined, or base metal. The electrode supplies filler material for making the weld, gas for shielding the molten metal from the air, and flux for refining this metal. Submerged-arc welding fuses the parts to be joined by the heat of an electric arc struck between a bare metal electrode and base metal. The weld is shielded from the air by flux. The electrode or a supplementary welding rod supplies metal filler for making the weld. Gas-metal-arc welding produces fusion by the heat of an electric arc struck between a filler-metal electrode and base metal, while the molten metal is shielded by a gas or mixture of gas and flux. For structural steels, the gas may be argon, argon with oxygen, or carbon dioxide. Electroslag welding uses a molten slag to melt filler metal and surfaces of the base metal and thus make a weld. The slag, electrically conductive, is maintained molten by its resistance to an electric current that flows between an electrode and the base metal. The process is suitable only for welding in the vertical position. Moving, water-cooled shoes are used to contain and shape the weld surface. The slag shields the molten metal. Electrogas welding is similar to the electroslag process. The electrogas process, however, maintains an electric arc continuously, uses an inert gas for shielding, and the electrode provides flux. Stud welding is used to fuse metal studs or similar parts to other steel parts by the heat of an electric arc. A welding gun is usually used to establish and control the arc, and to apply pressure to the parts to be joined. At the end to be welded, the stud is equipped with a ceramic ferrule, which contains flux and which also partly shields the weld when molten. Preheating before welding reduces the risk of brittle failure. Initially, its main effect is to lower the temperature gradient between the weld and adjoining base metal. This makes cracking during cooling less likely and gives entrapped hydrogen, a possible source of embrittlement, a chance to escape. A later effect of preheating is improved ductility and notch toughness of base and weld metals and lower transition temperature of weld. When, however, welding processes that deposit weld metal low in hydrogen are used and suitable moisture control is maintained, the need for preheat can be eliminated. Such processes include use of lowhydrogen electrodes and inert-arc and submerged-arc welding. Rapid cooling of a weld can have an adverse effect. One reason that arc strikes that do not deposit weld metal are dangerous is that the heated metal cools very fast. This causes severe embrittlement. Such arc strikes should be completely removed. The material should be preheated, to prevent local hardening, and weld metal should be deposited to fill the depression. Pronounced segregation in base metal may cause welds to crack under certain fabricating conditions. These include use of high-heat-input electrodes, such as the 1/4-in E6020, and deposition of large beads at slow speeds, as in automatic welding. Cracking due to segregation, however, is rare with the degree of segregation normally occurring in hot-rolled carbon-steel plates. Welds sometimes are peened to prevent cracking or distortion, though there are better ways of achieving these objectives. Specifications often prohibit peening of the first and last weld passes. Peening of the first pass may crack or punch through the weld. Peening of the last pass makes inspection for cracks difficult. But peening is undesirable because it considerably reduces toughness and impact properties of the weld metal. (The adverse effects, however, are eliminated by a covering weld layer.) The effectiveness of peening in preventing cracking is open to question. And for preventing distortion, special welding sequences and procedures are simpler and

The VAV concept as applied to air conditioning is based on the idea of varying the supply-air volume, with constant temperature, to meet changing load conditions of interior spaces or zones (Fig. 13.38). Many installations utilize packaged roof units, although large or small built-up units may also be used. Rooftop units may be used for the following VAV applications: 1. Interior VAV cooling and perimeter radiation 2. Interior VAV cooling and constant-volume perimeter heating 3. Interior VAV cooling with constant-volume, perimeter-heating, fan-coil units 4. Interior VAV cooling with fan-powered perimeter heating or cooling 5. Interior VAV cooling with perimeter VAV reheat 6. Interior VAV cooling, double-duct, with VAV perimeter cooling and heating These systems vary widely in advantages and disadvantages and should be analyzed very carefully in the preliminary stages of design for each project. 13.31.1 Zoning of Building Interiors Zoning is very important in the design stage and will contribute greatly to the success or failure of the HVAC system. An insufficient number of zones will lead to loss of temperature control in areas that do not have the controlling thermostat. The more zones utilized, the better will be the comfort conditions attained, but with some increase in initial costs. 13.31.2 Air Distribution All types of diffusers (registers) may be used with VAV control units. Standard diffusers with reduced air-flow rates, however, often cause dumping of discharge air directly downward with wide variations in space temperature. Many authorities recommend linear-slot-type diffusers to negate dumping. Such diffusers discharge air into the room with a horizontal flow that hugs the ceiling. This is called the coanda characteristic effect and is very effective in distributing supply air throughout