Method of testing timber connector joints
2004 Edition

Under IS 4907 (2004), the minimum distances for timber connectors are as follows: the end distance, measured parallel to the grain in the load direction, must be at least 1.75 times the connector's diameter, or for non-circular connectors, the full dimension in the load direction. The edge distance, measured perpendicular to the grain, should be at least equal to the connector's diameter, or the full dimension for non-circular connectors. For sloping end cuts, the perpendicular distance from the connector center to the sloping end must not be less than the required edge distance to ensure proper embedment and prevent splitting.

The load-slip behavior is evaluated by first applying a slow initial load of approximately 200 kg, which is then released to allow the connector to settle. Subsequently, the load is increased at a steady strain rate with slip measured using a dial gauge graduated to 0.02 mm at each load increment. A load versus slip curve is plotted until the maximum load or continuous slip without load increase is observed. From this curve, the proportional limit load and corresponding slip are determined. All measurements and observations are recorded in a standardized data sheet, ensuring consistent evaluation of joint performance.

IS 4907 encompasses a variety of metallic timber connectors including split rings, toothed rings, clamping plates, shear plates, and claw plates, as well as improvised metal rings made from mild steel pipe sections. Testing is performed on timber grouped into three categories based on compressive strength: Group A (Sal), Group B (Teak), and Group C (Chir), with strength variations of approximately ±30%. This classification ensures that connector performance is assessed across timbers with differing mechanical properties.

For multiple connectors, IS 4907 specifies testing on three-member joints fitted with two identical connectors. The thickness of each side member is generally half that of the central member, except for split rings where it is two-thirds. The central member's width should be at least twice the connector's width. Testing must follow the procedures outlined in Annex C, with additional special tests as detailed in Annex B if necessary. This ensures consistent and reliable evaluation of joint behavior under multiple connector configurations.

The standard recommends that the movable head of the testing machine should advance at a uniform speed of 0.6 mm per minute to maintain a constant strain rate during the load application. Initially, a slow load of around 200 kg is applied and then released to settle the joint. Load increments are then applied at intervals to enable slip measurements until the maximum load or continuous deformation without load increase occurs. This controlled loading rate facilitates accurate determination of the joint's proportional limit and strength characteristics.