Type M mortar Type S mortar Type N mortar Type O mortar Type PL or PM mortar Solid masonry of brick or other solid units: 8000 psi 400 350 300 200 4500 to 8000 psi 250 225 200 150 2500 to 4500 psi 175 160 140 100 1200 to 2500 psi 125 115 100 75 Grouted solid masonry of brick or other solid units: 8000 psi 500 4500 to 8000 psi 350 2500 to 4500 psi 275 1200 to 2500 psi 225 Solid masonry of through-the-wall solid units: 8000 psi 500 400 300 4500 to 8000 psi 350 275 200 2500 to 4500 psi 275 200 150 1200 to 2500 psi 225 175 125 Masonry of hollow units: 1000 psi 100 90 85 700 to 1000 psi 85 75 70 Piers of hollow units, cellular spaces filled 105 95 90 Hollow walls (cavity or masonry bonded): Solid units: 4500 psi 180 170 140 2500 to 4500 psi 140 130 110 1200 to 2500 psi 100 90 80 Hollow units: 1000 psi 80 70 65 700 to 1000 psi 70 60 55 Stone ashlar masonry: Granite 800 720 640 500 Limestone or marble 500 450 400 325 Sandstone or cast stone 400 360 320 250 Rubble, coursed, rough or random 140 120 100 80 * See also Tables 11.5 and 11.6. Allowable bearing stress directly under concentrated loads may be taken 50% larger than the tabulated

With the net factored soil-pressure distribution known, the factored shears and moments can be determined (Fig. 9.46d and e). Critical sections for shear and moment are shown in Fig. 9.46a. The critical section for two-way shear is at a distance d/2 from the columns, where d is the effective depth of footing. The critical section for one-way shear in both the longitudinal and transverse direction is at a distance d from the column face. FIGURE 9.47 Design conditions for a strap footing. Maximum negative factored moment, causing tension in the top of the footing, will occur between the columns. The maximum positive factored moment, with tension in the bottom of the footing, will occur at the face of the columns in both the longitudinal and transverse direction. Flexural reinforcement can be selected as shown in Art. 9.46. For economy, combined footings should be made deep enough to avoid the use of stirrups for shear reinforcement. In the transverse direction, the bottom reinforcement is placed uniformly in bands having an arbitrary width, which can be taken as the width of the column plus 2d. The amount at each column is proportional to the column load. Size and length of reinforcing bars must be selected to develop the full yield strength of the steel between the critical section, or point of maximum tension, and the end of the bar (Art. 9.49.4). When the distance between the two columns to be supported on a combined footing becomes large, cost increases rapidly, and a strap footing, or cantilever-type footing, may be more economical. This type of footing, in effect, consists of two footings, one under each column, connected by a strap beam (Fig. 9.47). This beam distributes the column loads to each footing to make the net soil pressure with unfactored loads uniform and equal at each footing, and with factored loads uniform but not necessarily equal. The center of gravity of the actual column loads should coincide with the centroid of the combined footing areas. The strap beam is usually designed and constructed so that it does not bear on the soil (Fig. 9.47b). The concrete for the beam is cast on compressible material. If the concrete for the strap beam were placed on compacted soil, the resulting soil pressure would have to be considered in design of the footing. The strap beam, in effect, cantilevers over the exterior column footing, and the bending will cause tension at the top. The beam therefore requires top flexural reinforcement throughout its entire length. Nominal flexural reinforcement should be provided in the bottom of the beam to provide for any tension that could result from differential settlement. The top bars at the exterior column must have sufficient embedment length to develop their full yield strength. If the distance between the interior face of the exterior column and the property-line end of the horizontal portion of the top bar is less than the required straight bar tension development length, the top bars should have standard end hooks to provide proper anchorage (Art. 9.49.5). Strength-design shear reinforcement [Eq. (9.40a)] will be required when Vu  Vc, and requirements for minimum shear reinforcement [Eq. (9.81)] must be observed when Vu  Vc /2, where Vc
shear carried by the concrete (Art. 9.47). For the strap footing shown in Fig. 9.47, the exterior column footing can be designed as a wall spread footing, and the interior column footing as an individualcolumn spread footing (Arts. 9.75 and 9.76). A mat or raft foundation is a single combined footing for an entire building unit. It is economical when building loads are relatively heavy and the safe soil pressure is small (See also Arts. 9.73 and 9.74.) Weight of soil excavated for the foundation decreases the pressure on the soil under the mat. If excavated soil weighs more than the building, there is a net decrease in pressure at mat level from that prior to excavation. When the mat is rigid, a uniform distribution of soil pressure can be assumed and the design can be based on a statically determinate structure, as shown in Fig. 9.48. (See Suggested Analysis and Design Procedures for Combined Footings and Mats, ACI 336.2R, American Concrete Institute.) If the centroid of the factored loads does not coincide with the centroid of the mat area, the resulting nonuniform soil pressure should be used in the strength

When flat sheets are used, precautions should be taken to prevent water from penetrating splices and intersections. The sheets may be installed in sash like window glass, or the splices may be covered with battens. Edges of metal sheets may be flanged to interlock and exclude wind and rain. Pressed-metal panels, mostly with troughed or boxed cross sections, are also used to form lightweight walls. Provision should be made in all cases for expansion and contraction with temperature changes. Allowance for movement should be made at connections. Methods of attachment vary with the type of sheet and generally should be carried out in accordance with the manufacturers recommendations. Applied like plaster, stucco is a mixture of sand, portland cement, lime, and water. Two coats are applied to masonry, three coats on metal lath. The finish coat may be tinted by adding coloring matter to the mix or the outside surface may be painted with a suitable material. The metal lath should be heavily galvanized. It should weigh at least 2.5 lb / yd2, even though furring strips are closely spaced. When supports are 16 in c to c, it should weigh 3.4 lb /yd2. (See Table 11.9 in Art. 11.25.6). The lath sheets should be applied with long dimensions horizontal and should be tied with 16-ga wire. Edges should be lapped at least 1 in, ends 2 in. The first, or scratch, coat should be forced through the interstices in the lath so as to embed the metal completely. In three-coat applications, the coat should be at least 1/2 in thick. Its surface should be scored to aid bond with the second, or brown, coat. That coat should be applied as soon as the scratch coat has gained sufficient strength to carry the weight of both coats, usually after about 4 or 5 hr from completion of the scratch coat. The second coat should be at least 3/8 in thick. It should be moist cured for at least 48 hr with fine sprays of water and then allowed to dry for at least 1 week. The finish coat should be at least 3/8 in thick. (When only two coats are used, for example, on a masonry base, the base coat should be a minimum of 3/8 in thick and the finish coat, 1/4 in. Before application of the base coat, a bond coat, consisting of one part portland cement and one to two parts sand, should be dashed on the masonry with a stiff brush and allowed to set.) For both the scratch and brown coats, the mix, by volume, may be 1 part portland cement to 3 to 5 parts sand, plus hydrated lime in amount equal to 25% of the volume of cement. Masonry cement may be used instead of portland cement, but without addition of lime, inasmuch as masonry cement contains lime. The finish coat may be a factory-prepared stucco-finish mix or a job mix of 1 part white portland cement, not more than 1/4 part of hydrated lime, 2 to 3 parts of a lightcolored sand, and mineral oxide pigment, if desired. Ingredients should be thoroughly mixed dry. Then, water should be added and the materials mixed for at least 5 mm in a power mixer. The first two coats usually are applied with a trowel. The finish coat may be sprayed or manually applied. (Plasterers Manual, EBO49M, Portland Cement Association.) In contrast to siding in which a single material forms the complete wall, precast concrete or metal and glass are sometimes used as the facing, which is backed up with insulation, fire-resistant material, and an interior finish. The glass usually is tinted and is held in a light frame in the same manner as window glass. Metal panels may be fastened similarly in a light frame, attached to mullions or other secondary framing members, anchored to brackets at each floor level, or connected to the structural frame of the building. The panels may be small and light enough for one man to carry or one or two stories high, prefabricated with windows. Provision for expansion and contraction should be made in the frames, when they are used, and at connections with building members. Metal panels should be shaped so that changes in surface appearance will not be noticeable as the metal expands and contracts. Frequently, light-gage metal panels are given decorative patterns, which also hide movements due to temperature variations (canning) and stiffen the sheets. Flat sheets may be given a slight initial curvature and stiffened on the rear side with ribs, so that temperature variations will only change the curvature a little and not reverse it. Or flat sheets may be laminated to one or more flat stiffening sheets, like mineral-fiber panels or mineral-fiber panels and a second light-gage metal sheet, to prevent canning. It may be desirable in many cases to treat the metal to prevent passage of sound. Usual practice is to apply a sound-absorbing coating on the inside surface of the panel. Some of these coatings have the additional beneficial effect of preventing moisture from condensing on this face. Metal panels generally are flanged and interlocked to prevent penetration of water. A good joint will be self-flashing and will not require calking. Care must be taken that water will not be blown through weep holes from the outside into the building. Flashing and other details should be arranged so that any water that may penetrate the facing will be drained to the outside. (See also Art. 11.21.) Walls may be built of prefabricated panels that are considerably larger in size than unit masonry and capable of meeting requirements of appearance, strength, durability, insulation, acoustics, and permeability. Such panels generally consist of an insulation core sandwiched between a thin lightweight facing and backing. When the edges of the panels are sealed, small holes should be left in the seal. Otherwise, heat of the sun could set up sizable vapor pressure, which could cause