Effect of longitudinal joint on the shear-key of hollow core slab which function as an rigid diaphragm

Various types of reinforced concrete floors can be applied to building construction. The floor of the building can be made of cast in place or precast concrete. The floors should function as a rigid diaphragm, in order to distribute the lateral forces on the building frame. While the floor is made of precast concrete, especially those without overtopping, should be arranged in such a way to function as a diaphragm. In order for the precast slab can function as a diaphragm, the components must be connected to the building frame and between the component itself . Some of them are drag strut, boundary element (chord), transverse joint, collector and longitudinal joint. This paper will discuss the influence of the longitudinal joint shear key with some types. The test specimen is modeled as two HCS are mounted parallel to each other , then the both of HCS are combined with perimeter beams to obtain the same model with the actual conditions and simplify to execute. All models of the test specimen are made to represent the three types of shear key. The test specimen is loaded the shear force and observed the structure behavior and crack patterns.


Introduction
Various types of reinforced concrete floors can be applied to building construction.The floor of the building can be made of cast in place concrete or precast concrete.Some types of precast concrete floor including solid slab (full depth slab), half slab, double T slab dan hollow core slab (HCS).
The floors in tall buildings should function as a rigid diaphragm, in order to distribute the lateral forces on the building frame.These properties characters can be obtained, when using a cast in place concrete floor.While the floor is made of precast concrete, especially without overtopping, should be arranged in such a way to function as a diaphragm.
Hollow Core Slab (HCS) is a type of plate precast components that behave in one direction (one way slab).The width range of HCS between 80-120 cm, while the length varies with the size of the longest can up to 20 meters.
Because one way slab, so the HCS are supported by two beams at the both ends.The beams are part of the building structure.The other two sides are not connected to the parallel beam.
In order for the precast slab can function as a diaphragm, then the components must be connected to building frame associated with the building frame and between the component itself.Some of them named drag strut, boundary element (chord), transverse joint, collector and longitudinal joint.
Longitudinal joint shear key form can be filled with materials or other components.There are three types of shear key that mortar, longitudinal reinforcement and shear reinforcement are mounted transversely.

Theory and design
Hollow core slabs are used as floor or roof to support vertical loads.But besides that also functions as a diaphragm to restrain and distribute lateral loads Lateral load be caused lateral pressure, wind loads or seismic loads.The main problem in planning the hollow core connection diaphragm is design to distribute the load to the diaphragm, the strength and ductility of slab system to carry the loads to the lateral load-bearing element.

Diaphragm element
x Boundary element : edge element around the diaphragm or perimeter of the diaphragm opening and together that bind together.Boundary element described as the pull rod / push (chord) or slider (drag strut).x Collector : element that distribute the shear force of the diaphragm to the lateral retaining elements.x Chord : Pull or push elements as a result of the behavior of the wing on the diaphragm to produce bending in the integrity of the diaphragm.The diaphragm must have the strength to distribute lateral loads imposed on the point to the point of lateral load resisting.Spans of the diaphragm between the lateral anchoring element behaves as a high beam and tied arch.

Longitudinal connection
Shear keyway are grouted between the slab has the capacity to distribute the longitudinal shear forces from one slab to the next slab.With shear stress 0.55 MPa, the nominal shear forces is If the grout strength is exceeded or ductile behavior is required, in principle, the sliding friction can be used to plan reinforcement is placed perpendicular to the longitudinal joint.This reinforcement can be placed on a transverse joint at the end of the slab rather than distributed throughout the connection.

Discussion and analysis
The test load F acts on the test object as figure 3D.But the style is observed is the force exerted on the joints between panels HCS Therefore, these forces should be determined by structural analysis.Oleh karena itu gayagaya tersebut harus ditentukan dengan analisa struktur.Structure of HCS is modeled as two shell elements are tied with boundary elements, so that a single unitary structure.Structural analysis is done by SAP2000.BU-1 has no reinforement.Testing load is 574.87 kN.From structural analysis, the axial force is 56.41 kN at shear key.
Shear strength of longitudinal connection without reinforcement can be calculated with equation (1).
The forces as testing result is 56.41 kN > 37.17 kN.These results indicate that the shear key without reinforcement and using only rely bond between shear key and concrete fillers give good results.
The magnitude of the deflection is small indicates that the structure is not deformed significantly

Conclusion
1. Installation and additional longitudinal reinforcement (BU-2 and BU-3) on the shear key does not give the shear strength significantly, but to improve its performance in terms of ductility.2. Transverse reinforcement BU-4 dan BU-5 in this study does not give a significant increase compared to BU-2 and BU-3, but get a good ductility.The increase is not significant be caused the number of possibilities that only one set of reinforcement.
Besides the possibility of anchoring insufficient, can affect the shear strength.3. Longitudinal shear key between HCS with 2 or more longitudinal reinforcement likes type 3 can be used for HCS diaphragm.This reinforcement must be anchored to the supporting beam.One advantage of this system is the ease of implementation.

Table 1 .
Test Result