1917 (#619-628) - Laserfiche WebLink

Home Browse Search

186 Beams and joists shall be figured to have a deflection of not more than 1/360 of the span under full load. Maximum fibre strain for Washington fir or what is known ordinarily as Oregon pine, must not exceed 1200 lbs, per sq. in. Where beams are short, their carrying capacity must be determined by their crushing strength at the bearings, and on long beams their carrying capacity must be figured so as not to exceed the deflection given above where plastered ceilings are used. Joists or girders shall not be cut in any manner for pipes or other purposes and where joists are the minimum depth re- quired for the span, they shall not be cut on the upper side more than one foot distant from the bearing partitions on which they rest. Where joists or timbers are cut for the purpose for running plumbing or steam pipes, piping or for other purposes such joists and timbers must be properly framed to sustain all floor levels as required by this Ordinance. Every wood beam except header beams must have a bearing at each end at lea~t 4 inches long and every girder or truss shall have a bearing of not less than g inches long. The maximum trussing strength on joist and similar bearings shall not exceed 500 pounds per square inch. Where joist ends rest in a masonry wall the ends shall be cut to a bevel of at least 3 inches in their depth. All timbers, columns and posts in mill or post and girder construction must be cut square at both ends at right angles to their axes, and capped with timber or iron or steel caps and provided with base plates. Where the cap plate of a wood post supports a wood girder and a p~ t above, the bottom of the upper post shall extend to and rest on the cap of the post below, and posts and corbels must be r&gidly fastened to each other so that in case of failure of beam resting on one side of corbel, the beam on the other end will be held in place. All beams must be self-releasing and in any case when floor load exceeds 75 lbs. per sq. ft. iron or steel bolsters shall be used and bolted or lag screwed to column in such a way as ~o make a rigid connection. And beams must be so fastened as to make a~ie but be self releasing in case of fire. Corbels of wood may be used in post and girder construction where wooden posts and beams are employed but the safe crushing strength of the material must not be exceeded. Every wood header beam more than 4 ft. long used in any building except Class "D" construction shall be suitably framed and hung to the trimmer beams and stirrup irons of proper thickness, for the size of timber. Ends of tail beams shall be properly framed into the header beams or shall be carried with stirrup irons hung on the header beams. These requ~ements shall not necessarily be enforced in residence work. Studs in Class "D" buildings must not be less than 2 X 4 inches for the upper two stories and lower stories not less than 2 X 6 inches. The distance on centers in any case to be not more than 16 inches. In three story buildings 3 X 4 studs may be substituted for 2 X 6 in the lower story. Studding in all outside walls and main bearing partitions must be placed with the greatest dimension at right angles to the ~urse of wall. In non bearing partitions and one-story cottages having not more than 12 foot etude the studs may be 2 X 3 inches, shall be double width where plumbing is used, or 2" X 6" studs may be used. In bearing partitions a single 2 inch plate may be used underneath the studs, but at least a double 2 inch plate must be used for the top plate when the construction is carried up story by story. Where the span of wood joists exceeds g ft. there must be at least one row of 1 X 4 inch or 1} X 3 inch or 2 X 2 inch cross bridging for every 12' O" of span or fraction thereof. When Joists are lathed and plastered or concealed the block or fire stop not less than 2" thick must be cut in between the Joists over each bearing partition completely filling the space. Every stud partition over 9' high shall have a 2" bridging or fire stop, the full width of the studs cut in midway between floor and ceiling and when plates are not used for any height of studs there must be a 2 inch fire stop at top and bottom. In all buildings over one story high the joists must be securely tied to each other making a continuous tie from wall to wall and where Class "B" or Class "C" construction is used proper means must be taken to tie joists to masonry walls as specified under masonry construction. Where posts and girders are used under small buildings of Class "D"constr~ction the posts must be at least 4 X 4, spaced not more than 6' centers and no girder shall be less than 4 X 4". Rafters in class "B" or "C" buildin[s shall not be placed further apart than 24" on centers, and must be covered with boarding not less than 1" thick. All roofs in Class "B" or "C" buildings shall bs covered with metal or some fire resis- ting composition roofing. Section 20. Buildings of Class "D" construction over one story in height shall have a continuous masonry founda- tion not less than g" thick below floor level and extend not less than 6" above finished grade. If such foundation is not more than 10' high it must be 6" thick if built of brick or 6" thick if built of concrete, and for every successive 10' of height below the top 10' the walls shall be increased 4 inches in thickness.