Prestressed anchor tensioning procedures and requirements!

Prestressed anchor tensioning procedures and requirements!

1. Check concrete components and channels

Before the tension equipment, check whether the position of the pad is accurate, whether the surface is flat, and whether it is perpendicular to the anchor hole end, such as the anchor plate and the hole end are not vertical, on the one hand, stress loss, on the other hand, due to the stress concentration pressure of the anchor concrete, resulting in tension failure, causing immeasurable loss, there are no shortage of examples of such lessons. For the passage before pouring, check whether the strand can slide freely in the passage.

2. Tensioning sequence and tensioning method

The tension sequence shall conform to the design regulations. The tensioning method is generally used at both ends. When the hole is short, single-end tensioning can be used. When conditions do not allow both ends to be tensioning, single-end tensioning is also used. However, the stress loss of prestressed anchors is great when they are tensioned at one end, so measures must be taken to reduce the stress loss. Only one hole can be stretched at each end, and the other two holes can only be stretched at one end. However, due to the length of the hole, the friction resistance of the single-end tensioning hole is large, and there is no successful precedent for whether the stress can be successfully transmitted to the other end and how much it can be transmitted. In order to obtain scientific data, when both ends of hole No. 1 are tensioned, single-end tensioning test is used, and the main hole friction resistance test is carried out. It is obtained that the tensioning tension transfer of one-end straightening wire harness is 73.34%, and the tensioning tension transfer of curve bundle is 52.4%, which is far from meeting the requirements of tensioning stress. By adding soapy water to reduce the friction resistance test, the stress transfer is 83.85%, an increase of 16.48%, which can basically meet the tension requirements. As the single-end tension test of the first hole provided first-hand scientific data, the last two holes used soapy water to reduce the friction resistance of the hole, and the tension and elongation met the requirements, solving the contradiction of single-end tension transmission, and the tension was successful.

3. Tensioning procedure

The general tensioning procedure is: 0→ initial stress σ0→105σK→σK(anchor) where :σK is the control stress during tensioning, including the expected value of prestress loss.

Note: When the tension between the two ends is applied, the lifting pressure, marking and elongation measurement of the jack at both ends should be consistent. The tension adopts "double control", that is, the control tension and elongation, and the elongation should be designed to be within ±6% of the elongation, otherwise the cause should be identified.

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