moisture conditions* T  100
F 100
F  T  125
F 125
F  T  150
F Dry 1.0 0.8 0.7 Wet 1.0 0.7 0.5 *Wet and dry service conditions are defined in a Table 10.29 footnote. 1. Two or more split-ring or shear-plate connectors aligned with the direction of the load. 2. Two or more bolts with the same diameter, loaded in shear, and aligned with the direction of the load. 3. Two or more lag screws of the same type and size loaded in single shear and aligned with the direction of the load. When fasteners in adjacent rows are staggered but close together, they may have to be treated as a single row in determination of Cg. This occurs when the distance between adjacent rows is less than one-fourth of the spacing between the closest fasteners in adjacent rows. The group-action factor is necessary because of the following characteristics of a joint with more than two fasteners in a row: The two end fasteners carry a larger load than the interior fasteners. With six or more fasteners in a row, the two end fasteners may carry more than 50% of the load. With bolts, a small redistribution of load from the end bolts to the interior bolts occurs due to crushing of the wood at the end bolts. If failure is in shear, a partial failure occurs before substantial redistribution of load takes place. 10.14.5 Geometry Factor The NDS specifies minimum edge distance, end distance, and spacing required for full design value for bolts, lag screws, and split-ring and shear-plate connectors. The NDS also tabulates nominal design values for these fasteners based on the minimum distances. When the end distance or the spacing is less than the minimum required for full design value but larger than the minimum required for reduced design value, nominal design values should be multiplied by the smallest applicable geometry factor C determined from the end distance and spacing requirements for the type of connector specified. The smallest geometry factor for any connector in a group should be applied to all in the group. For multiple shear connections or for asymmetric three-member connections, the smallest geometry factor for any shear plane should be applied to all fasteners in the connection. The NDS also outlines geometry factors for timber rivet connections loaded perpendicular to grain. 10.14.6 Penetration-Depth Factor Nominal lateral design values for lag screws, wood screws, nails, and spikes are based on a specific penetration into the main member, as established by the shank TABLE 10.31 Group-Action Factors (a) For bolt or lag-screw connections with wood side members*

Superplasticizers are high-range water-reducing admixtures that meet the requirements of ASTM C494 Type F or G. They are often used to achieve highstrength concrete by use of a low water-cement ratio with good workability and low segregation. They also may be used to produce concrete of specified strengths with less cement at constant water-cement ratio. And they may be used to produce self-compacting, self-leveling flowing concretes, for such applications as longdistance pumping of concrete from mixer to formwork or placing concrete in forms congested with reinforcing steel. For these concretes, the cement content or watercement ratio is not reduced, but the slump is increased substantially without causing segregation. For example, an initial slump of 3 to 4 in for an ordinary concrete mix may be increased to 7 to 8 in without addition of water and decrease in strength. Superplasticizers may be classified as sulfonated melamine-formaldehyde condensates, sulfonated naphthaline-formaldehyde condensates, modified lignosulfonates, or synthetic polymers. 4.13.2 Air-Entraining Admixtures These create numerous microscopic air spaces within concrete to protect it from degradation due to repeated freezing and thawing or exposure to aggressive chemicals. For concrete exposed to repeated cycles of freezing and thawing, the air gaps provide room for expansion of external and internal water, which otherwise would damage the concrete. Since air-entrained concrete bleeds to a lesser extent than non-air-entrained, there are fewer capillaries extending from the concrete matrix to the surface. Therefore, there are fewer avenues available for ingress of aggressive chemicals into the concrete. The Standard Specification for Air-Entraining Admixtures for Concrete, ASTM C260, covers materials for use of air-entraining admixtures to be added to concrete in the field. Air entrainment may also be achieved by use of Types IIA and IIIA portland cements (Art. 4.2.2). 4.13.3 Set-Accelerating Admixtures These are used to decrease the time from the start of addition of water to cement to initial set and to increase the rate of strength gain of concrete. The most commonly used set-accelerating admixture is calcium chloride. Its use, however, is controversial in cases where reinforcing or prestressing steel is present. The reason is that there is a possibility that the accelerator will introduce free chloride ions into the concrete, thus contributing to corrosion of the steel. An alternative is use of one of many admixtures not containing chloride that are available. 4.13.4 Retarding Admixtures To some extent, all normal water-reducing admixtures retard the initial set of concrete. A Type B or D admixture will allow transport of concrete for a longer time before initial set occurs. Final set also is delayed. Hence, precautions should be taken if retarded concrete is to be used in walls. Depending on the dosage and type of base chemicals in the admixture, initial set can be retarded for several hours to several days. A beneficial side effect of retardation of initial and final sets is an increase in the compressive strength of the concrete. A commonly used Type D admixture provides higher 7- and 28-day strengths than a Type A when used in the same mix design. 4.13.5 Mineral Admixtures Fly ashes, pozzolans, and microsilicates are included in the mineral admixture classification (Arts. 4.9 and 4.10). Natural cement (Art. 4.4) is sometimes used as an

Diaphragm construction Masonry and concrete walls Wood and light steel walls Concrete Limited by deflection Steel deck (continuous sheet in a single plane) Steel deck (without continuous sheet) 2:1 21/2:1 Cast-in-place reinforced gypsum roofs 3:1 4:1 Plywood (nailed all edges) 3:1 4:1 Plywood (nailed to supports onlyblocking may be omitted between joists) Diagonal sheating (special) 3:1 31/2:1 Diagonal sheating (conventional construction) *From California Administrative code, Title 21, Public Works. Use of diagonal sheathed or unblocked plywood diaphragms for buildings having masonry or reinforced concrete walls shall be limited to one-story buildings or to the roof of a top story. FIGURE 5.86 Distribution of horizontal load to parallel shear walls: (a) walls with the same length and rigidity share the load equally; (b) wall half the length of another carries less than one-eighth of the load. obtained from Eq. (5.149), with H/L  4/4  1. For any one of the piers, the