DOB Findings and Recommendations for WTC, Feb 2003

NYC 9/11 Public Portal Document

iii. Bars projecting from the ends of the precast members may be joined by lapping of bars, reinforcement grouted into apertures, overlapping reinforcement loops, sleeving, threading of reinforcement or welding of bars. iv. Bars lapped with cast-in-place topping or connecting concrete to form a continuous reinforcement with projecting links from the support of the precast floor or roof members to anchor such support to the topping or connecting concrete. 3. Joints transmitting compression should be designed to resist all the forces and moments implicit in analyzing the structure as a whole and in designing the individual member to be joined. 4. Joints transmitting shear in-plane may be assumed effective if the joint is grouted with a suitable concrete or mortar mix and should not require restraint if the design ultimate shear stress in the joint does not exceed 34-psi. 5. Joints transmitting shear under compression in all design conditions may be assumed effective if the joint is grouted with the sides or ends of the panels-forming the joint have a rough as-cast finish and the design ultimate shear stress does not exceed 67 psi 6. Joints transmitting shear may be assumed effective if the shear stresses due to ultimate loads is less than 192-psi calculated on the minimum root area of a castellated joint. Separation of the units normal to the joints should be prevented by either steel ties across the ends of the joint or by the compressive force normal to the joint under all loading conditions. 7. Joints transmitting shear may be assumed effective if reinforcement is provided to resist the entire shear force due to design ultimate loads. The shear force should not exceed O.SFttanOf where Fb is the lesser of O.PSfyAj or the anchorage value of the reinforcement. As is the minimum area of reinforcement and cq is the angle of internal friction between the faces of the joint. The values of Of for concrete connections are 0.7 for a smooth interface, 1.4 for a roughened or castellated joint without continuous in situ strips across the ends of the joints and 1.7 for a roughened or castellated joint with continuous in situ strips across the ends of the joints. C) In steel frame structures, horizontal ties should be arranged in continuous lines wherever practical, distributed throughout each floor and roof level in two perpendicular directions. 1. Every steel member should act as a horizontal tie, and their connections should be capable of resisting a tensile force equal to its end reaction under factored loads (or the ■ larger end reaction if they are unequal), which need not be considered additive to other loads. 2. The horizontal ties anchoring all columns should be capable of resisting a factored tensile load, acting horizontally in any direction, equal to the greater of the end reactions under factored loads or 2% of the maximum factored vertical dead and live load in the column adjacent to that level. Where multiple members frame in one direction, no connection should be less than 1% of the column load. 3. If columns are not continuous then the frame should be detailed to provide full continuity to the columns. 4. Each column splice should be capable of resisting a tensile force equal to the largest factored vertical dead and live load reaction applied to the column at ten floor levels located immediately below that column splice or 2/3 of the column capacity whichever is smaller. 5. Braced bays or other systems for resisting lateral loads should be distributed throughout the building.

D) In masonry structures: 1. Peripheral horizontal ties, should be provided along the whole perimeter within 4-feet of slab edge, and anchored at reentrant comers. The design capacity is 3.3F,. 2. Interior horizontal ties should be provided both ways either uniformly or in strips no farther apart than 20-feet or in walls no farther than 1.6-feet from floor or roof. The design strength along the width is the greater of Ft or (2F,)(DL+LL)(La/5) per unit width*^\ where DL and LL are the dead and live load expressed in ksf, L, is lesser of the February 2003 WTC Building Code Task Force Page 33 Findings and Recommendations

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