Shallowly discusses the construction joint processing
Introduction
Massive engineering structure shakes harms the example to indicate that, the portal frame construction pitch point universal destruction is heavier, often causes the structure to expire, the Chinese and foreign scholar analyzes indicated, this is the various reason, including the design fault, has not strengthened the pitch point intensity, realizes reason and so on strong pitch point strong anchor. Simultaneously constructs also has the construction quality weakness, difficulty with guarantees the design anticipated target. In construction new old concrete construction gap time, continues the surface position, continues the surface processing method, the new old coagulation locally born ripe ingredient and inspires pounds the influence pitch point caking intensity which the control quality all makes, therefore in portal frame construction project construction process, because in each pillar construction inevitably and the lower level pillar existence construction joint, how does leave alone the construction joint, how processes the construction joint, causes the project quality not to receive affects, guaranteed concrete the structure security, appears especially importantly.
1.current portal frame construction pitch point job practice and the flaw.
(1) the early time in the general portal frame construction, after pours a pillar, carries on a mold, after the template installment completes only then enters sewer the working procedure to pour the upper formation girder concrete, therefore acts according to constructs the time limit for a project and the person, the material, machine and so on the situation, the new old concrete continues the gap time length not one, when pouring the general pitch point pours together along with the girder concrete, and the pitch point concrete intensity rank carries on the construction according to girder
(2) along with the scientific research development and the construction level enhancement, in particular specialized level higher big general contractor starts in view of steel construction the pitch point construction quality weak characteristic to take a series of measures, when pours the upper oration steel construction carries on chiseling processing with the drill rod front, pours carries on the watering to the old concrete to be moist, and in hands over in the composition plane with the high-grade cement mortar shop, steel construction the pitch point area concrete intensity rank generally uses the pillar (common pillar intensity and so on to rise), is pouring the pitch point zone time to strengthen inspires pounds and the strict control water-to-cement ratio. After a series of processing measure, the construction quality obtained the enhancement, but column the pitch point area concrete still was the construction weak area, is very difficult to obtain ideally continues the effect.
(3) although continued the spot to carry on processing, but its flaw was very obvious: First uses the drill rod to carry on chiseling processing, extremely shirt and old concrete, so that the old concrete produces the initial micro crack, seriously affects the new old concrete to continue the intensity, also chiseling processing difficulty with controls the processing quality specification front, pours to continues the spot moistly to carry on the watering to be very easy to work just the opposite, thus increased has handed over the composition plane place concrete water-to-cement ratio, but in handed over in the composition plane with the high-grade cement mortar shop to be very easy because the high-grade cement mortar and the green concrete hydro mass congealed and the contraction different, thus caused to continue the surface to be easier to have the initial stress and the initial micro crack. But pitch point area concrete intensity rank difference and girder, thus caused the column girder pitch point area actually to produce four frontal zones (although girder and pitch point area whole poured, but concrete intensity rank general different, thus also has created weak contact surface), when construction was very difficult to control inspires pounds the density and the time, was very easy because inspired pounds the depth but to injury and the old concrete, or because strengthened inspires pounds causes originally water-to-cement ratio to have the partial bleeding phenomenon on the quite small concrete, thus the influence concrete intensity growth, reduced the contact surface caking intensity.
2.Column pitch points areas destruction mechanism and the earthquake resistance
design request by shakes harms the investigation obviously, column the pitch point area destruction, mostly is because the pitch point area does not have stirrup or are few stirrup, in cuts presses under the function the concrete to appear the slanting crack even to extrude destroys, creates the longitudinal reinforcement buckling to become the lantern shape. Therefore, guaranteed the pitch point area not premature has the shearing failure main measure is guaranteed the pitch point area concrete the intensity and the density, is enough in the pitch point area disposition stirrup. The design column frequently uses the different rank the concrete, when the construction must pay attention to column the pitch point spot concrete rank to be supposed same or is slightly low with the column concrete rank (difference not to be able to surpass 5M pa). Thus realizes the strong pitch point strong anchor. In the vertical pressure and the girder end pillar end moment, under the shearing force function, the pitch point area has the more complex stress condition. Pitch point experiment which from unit and so on Beijing construction design institute carries on obviously, the pitch point destruction process approximately may divide into two stages: The first stag
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