According to the pouring speed and initial setting time, the lateral pressure of non-initial setting concrete is considered in the calculation formula. That is to say, under the same pouring speed, initial setting time, bulk density and other parameters, the lateral pressure of the formwork at any height is the largest (it can be considered that the lateral pressure of liquid concrete on the formwork is just from the initial setting surface to the current pouring height), but the pouring height is generally small. Until the pouring is completed, the first layer of concrete has not been initially set, or even far from the initial setting time.
Then the deviation between this value and the actual situation on the spot is great. Far greater than the actual situation. Type 2 is calculated according to the actual pouring height of all liquid concrete, so there may be slow pouring speed, initial setting, and the lower concrete that has not been poured has been initially set, and this part of concrete has no lateral pressure on the formwork.
The calculated result is also much larger than the actual value. For example, if the effective head is 4m, the calculation result according to formula 1 is applicable to the lateral pressure of formwork above 4m, and formula 2 is applicable to the lateral pressure of formwork below 4m. When it is more than 4 meters, the current pouring height is less than 4 meters, so it can be considered that there is no lateral pressure under the current conditions.
When it is less than 4 meters, it can be considered that the formwork is completely compressed. So take a small value according to two formulas. However, when substituting parameters, the most unfavorable conditions are considered, that is, the longest initial setting time and the fastest pouring speed.
Extended data:
The lateral pressure coefficient has a significant influence on the stability of tunnel surrounding rock, and also has a certain relationship with the tunnel section form. The displacement change of tunnel surrounding rock reflects the stability of tunnel surrounding rock to some extent.
Under the same lateral pressure coefficient, the greater the buried depth, the greater the displacement of key points of the tunnel. When the lateral pressure coefficient is large, the displacement is significantly affected by the increase of buried depth.
Under the same buried depth, when the lateral pressure coefficient is small, the displacement of tunnel surrounding rock is less affected by the lateral pressure coefficient, while when the lateral pressure coefficient is large, the displacement of tunnel surrounding rock changes obviously. When the buried depth and lateral pressure coefficient are maximum, the key points of maximum displacement of tunnels with different sections are located in different positions.
The load of fresh concrete on pier formwork is different from the gravity load of platform formwork, and the effect of fresh concrete pushing the lateral formwork horizontally is similar to that of water pushing the container wall. But unlike water pressure, concrete pressure is temporary. When the concrete is hard enough to support itself, this pressure disappears immediately.
The pressure variation law of each measuring point basically increases linearly in a certain period of time, then decreases slowly after reaching the peak value, and then increases slowly after the pressure stabilizes for a short period of time. In the process of concrete pouring, initial setting time and pouring speed are the main influencing factors, and after concrete pouring, temperature is the main influencing factor.
Concrete can be divided into heavy concrete, ordinary concrete and light concrete according to its apparent density. The difference between these three kinds of concrete is the difference of aggregate.
The apparent density of heavy concrete exceeds 2500 kg/m3, and it is made of particularly dense and heavy aggregate. Such as barite concrete and steel chip concrete. , not affected by x-rays and γ-rays; It is usually made of barite and iron ore.
Ordinary concrete is commonly used in buildings, and its apparent density is 1950 ~ 2500 kg/m3. Mainly made of sand and stone, it is the most commonly used concrete variety in civil engineering.
Light concrete is concrete with apparent density less than 1950kg/m3. It can be divided into three categories:
1. lightweight aggregate concrete, its apparent density is 800 ~ 1950kg/m3. Lightweight aggregate includes pumice, volcanic slag, ceramsite, expanded perlite, expanded slag and slag.
2. Porous concrete (foamed concrete, aerated concrete), its apparent density is 300 ~ 1000 kg/m3. Foam concrete is made of cement slurry or cement mortar and stable foam. Aerated concrete is made of cement, water and gas-generating agent.
3. Macroporous concrete (ordinary macroporous concrete and lightweight aggregate macroporous concrete) does not contain fine aggregate. The apparent density range of ordinary macroporous concrete is 1500 ~ 1900 kg/m3, which is made of crushed stone, soft stone and heavy slag. The apparent density of lightweight aggregate macroporous concrete is 500 ~ 1500 kg/m3, which is made of ceramsite, pumice, broken bricks and slag.
References:
Baidu encyclopedia-lateral pressure