In general, the problem of overall torsional balance of the spandrel beam represents most of the difficulties encountered by spandrel beams. Disturbance of twisting of the inner lamp beam is often observed, often within distance "d" from the ends of the beam. equilibrium bonds.
A variation of the same problems caused by torsional rolling of the vertebral beam (lack of torsional balance connections at the ends of the beam) is shown in Fig. A picture. Typically, the peak force of the H couple develops due to the bending behavior of the beam web.
The sill, or cap of a joist is the usual mechanism for transferring concentrated loads applied to the web of the beam, where the web in turn transmits these concentrated loads to the support reaction of the beam.
GENERAL DESIGN REQUIREMENTS
Torsional balance reinforcement at the end of the beam. The edge to the web can be done by the strength of ordinary concrete or by reinforcing steel, depending on the dimensions of the beam, the concrete strength and the magnitude of the edge load. The position of the load Vu can also affect the edge-to-web capability. The final fastening strength of an unreinforced ledge depends on the tensile strength of the concrete.
The reinforcement for attaching the lamp ledge to the web of the beam is shown in Fig. 22c, along with the parameters for determining the required amount of reinforcing steel. The ultimate shear stress in the vertical shear plane of the ledge when using steel A, (see Fig. 23b) should not exceed 10 k,f7. Ah at the end of the beam should limit the end of the ledge, and usually have a hairpin configuration that pivots on the continuous ledge A. The steel required by Eq. 11) is not additive to the struts required to resist web shear and torsion as it essentially reinforces another crack plane.
If the girder is not provided by additional beams, then special reinforcement must be used carefully anchored to the side of the web ledge. Two cases of web bending can develop if the overall rotational balance of the lamp beam is created by the beam web acting against its tip. The force w^„ acting against the web can be transferred from the bending of the web (see Fig. 24c) to the bottom of the web of the beam and then from the bottom of the web to the ends of the beam.
In turn, this horizontal ultimate bending behavior of the lower web section can be resisted by reinforcement, which is in addition to that required for vertical bending (see Fig. 24e). This modified behavior follows when the spandrel beam has adequate torsional reinforcement, proper bottom H, overall torsional equilibrium connections (see Fig. 24b), and the top connection is at the top plane (see Fig. 24a), but only a limited portion of the top layer at the beam side is involved in the development of H,. Reinforcement A„ in the beam web at the crown tip (see Fig. 25a) is required to produce the crown moment.
CONSIDERATIONS FOR CONNECTION DESIGN
Connection Systems
When using rebar for connections, attention must be paid to the influence of the bending radius (no rebar is bent at a right angle), welding requirements (chemical composition of the rod, electrodes with low hydrogen content and preheating). the rod configuration and placement tolerances. The element that must be adjustable to accommodate the tolerances involved is the size of the insert hole in the beam (see Fig. 30). a, and b, the location dimensions of the hole in the manufactured beam may vary at most from % to 'in.
The location of the column may be different than planned due to the location of the foundation or the position of the anchor bolts within the foundation. Shared bearing means that the bearing pad makes contact with both the concrete and the steel in the auditory area. Further, the details should illustrate the items that appear in the plane of the detail, in addition to other items that are perpendicular to the plane of detail.
The bond fitting interface requires three-dimensional assessments of all bond materials. Tee stein or stiffeners are needed to transfer the slack force of the slab directly to the embedment reinforcing bars. Additionally, the loose plate force distribution may not even be in the embedded reinforcing bars considering tolerance variations such as dimensional shifts in the placement of the connection hardware in the beam and column.
Typically, if the beam is subjected to gravity loads, the lateral stability connections of the frame should not be made until all or most of the dead load has been established. This is necessary if the proper stiffness of the column is to be correctly estimated. A change in column height of 3.5 ft (1.1 m) has a significant effect on the magnitude of the volume change forces induced in the frame connections and on the beam and column forces.
The location of the ledge tie reinforcement and all other beam tie reinforcing bars is important to the tie in developing its design strength. 203 mm) acting over the lesser horizontal length of eight times the grid width or the total height of the lamp beam.
GOOD DESIGN PRACTICE
In addition to the end connections, the column is attached directly to the horizontal diaphragms, as well as the beam for its lateral support. The spandrel beam's vertical span properties (see Fig. 41c) can be determined from the web width of 8 inches. The model (Fig. 41b) deals only with the additional column equilibrium forces to which the beam-to-column connections are subjected.
Another loading condition to examine is that resulting from volume change deformations acting parallel to the T-tube span. Instead of the rigid horizontal beams in Fig. 41b, the horizontal frame elements in Fig. 42 should be used to simulate the deformations of the volume change, so that the total forces on the connections can be determined. t, CURB TIED TO GRAM AND PILLAR Z. OTHERS SAME AS FIG. for the analysis of connection loads caused by column equilibrium deformations and volume changes.
Details must be prepared during design to ensure that the three-dimensional interface requirements for rebars are satisfied. 19 mm) between tension wire reinforcements in different levels should be planned to accommodate rebar tolerances and interfaces. Special welding requirements and procedures must be determined when welded reinforcing bars are used at critical connections.
Separate fabrication and placement tolerance estimates should be made for each design, rather than just relying on the "usual" industry tolerances. When selecting tolerance and distance requirements, the influence of structural deformations during installation must be taken into account. Designs should be based on selected tolerances and offsets that produce maximum forces.
Corrosion Protection
The arrangements and positions of the steel shall be such that ordinary workers can fabricate and construct them. Where possible, avoid using tension insertion connections to ensure spandrel beam torsional balance due to tolerances. Ensure that the connecting device can be practically integrated into the rod without interference or conflict with other materials within range.
Connections using loose field welded plates or threaded rods shall require the anchorage device embedded in the beam and/or adjacent member to have a load capacity one-third greater than the loose connection plate. Complete free-body diagrams should be developed for each connection model to ensure that all forces are accounted for and that statics are satisfied. Loads resulting from volume change deformations shall use the same ACI Code 1.7 load factor as required for live loads.
A load factor of at least the usual combined final dead and live load factor of 1.5) must be used for all vertebral beam connections. For connections relying on concrete shear cones for load-bearing capacity, a load factor of 3 should be used unless a lower load factor of 2.5 cannot be reasonably justified. The column loads arising from the torsional equilibrium connections of the vertebral beam and beam reaction should be analyzed to ensure the correct column design.
Column design requires that the influence of the column and the spandrel's actual size be considered throughout the analysis rather than just using simple beam-to-column centerline dimensions for the analysis. Connection reinforcements shall be inspected for placement position and arrangement by the designer or his representative during the manufacture of prestressed girder. Welded moment frame connection hardware embedded in tension wire (and columns) requires weld inspection and testing of the bar and plate welds.
CLOSING COMMENTS
ACKNOWLEDGMENTS
Note: An Appendix giving design examples is included following the Notation Section
NOTATION
H = horizontal applied load or horizontal torsional equilibrium connecting force, working or end point, lbs or kips. P„ = ultimate concentrated load applied to the beam ledge, lbs or kips R, R, Ra = support reaction at the end of the beam. Ybp = distance from the center of gravity of the bundle cross-section to the extreme bottom fiber along an inclined vertical line. 10 = ratio of final internal motion.
APPENDIX-DESIGN EXAMPLES
1.52 25.3 Find J1
- bar size per 12 in. spacing
- Steel ultimate = (4/3) (LF) (Working Load)
Summary
The calculated shear stress is therefore satisfactory as it is less than the recommended 800 psi maximum. Note that no edge attachment reinforcement is required due to beam reaction for end-T stem V. Add #4 stirrups so that additional stirrups plus shear and torsion stirrups 1.60 sq. in provided.
The ultimate load-bearing capacity of the concrete at the extreme edge of the edge may require the use of additional load-bearing reinforcement as shown in Fig. Assume a spindle support for a building with the configuration and dimensions shown in the cross section below.
