KR20030033108A - Method for demonstrating the supporting stability of supporting systems under fire load - Google Patents

Abstract

PURPOSE: A proving method of supporting stability of a support system against fire load is provided to check the supporting stability of the concrete structure under fire load during or after fire by calculating changes of material properties and residual strength based on staff statics without complex calculation. CONSTITUTION: A safety proving method proves the safety against collapse of load-bearing systems under fire load by calculating the changes of the material properties during the fire and the residual strength after the fire on the basis of data obtained by means of bar statics which are already obtained from the construction of the building component and which relate to the design of the building component for standard load cases such as dead load, loading in consequence of groundwater and of earth pressure, and living load. Fire load is defined(1), and temperature load of the cross section is calculated(2). The time stage and all time stages are calculated to define the condition after fire(3,4,5), and the demand is derived from the structure(6).

Description

METHOD FOR DEMONSTRATING THE SUPPORTING STABILITY OF SUPPORTING SYSTEMS UNDER FIRE LOAD}

Buildings subjected to static loads are generally designed to withstand adverse environmental effects for at least several hours, such as the rise in temperature loads that occur when a fire occurs.

To this end, for example, by lining the surface of the tunneling element with a heat insulating mat, it is possible to delay the heating of the tunnel sheet in the event of a fire.

Recent images of damage from tunnel fires have shown that not only reinforced concrete but also reinforced concrete supporting frameworks have supporting reserves to prevent the effects of fire. . However, a suitable calculation method for demonstrating such a support reserve on the basis of the same principle as the demonstration of oil pressure and other loads is not known until now.

However, because the national authorities require several times to present such proof during the accreditation process, the object of the present invention is to develop a calculation method that can be calculated without the use of complex numerical methods, during and after a fire. It is to be able to prove the supporting stability of hydrostatically loaded concrete structures.

In addition, a reliable information source will be provided that provides information on how long the concrete under fire load can remain stable before it collapses. This information is important to know how much time there is from the outbreak of fire to evacuation of people at risk or when it is no longer possible for firefighters to enter the fire site.

This problem in principle applies to all buildings subjected to hydrostatic loads. However, the present invention will specifically address the problem of fire occurring in tunnels. This proof of support stability is particularly important for tunnel installations in urban areas where tunnel rock can collapse to the constructed surface. This problem is more clearly seen by knowing that the distance between the ceiling and the ground of the tunnel is only a few meters, about 7 to 15 meters.

To consider the fire load and its effect on the supporting structure, the steps of analysis can be divided into three important parts:

-Definition of fire load

Calculate the temperature gradient of the part

-Proof of support stability of buildings

To define the fire load, one can employ either a predefined fire trend or a fire load curve that is specifically calculated in each case. In such cases, the type of cargo being transported or transported is considered. This fire load curve determines the temperature trend over time.

If the fire load is so pre-determined, the differential equation can be solved to calculate the temperature gradient of the part over time. In this case, a calculation program is provided to solve this thermal conduction problem.

Corresponding calculations of tunnel rock for the so-called standard loads, such as dead weight, water load, pressure of earth and working load, are presented early in the development of all structures. is average. Most of these calculations are done using linear staff statics. The demonstration of temperature loads is likewise made according to this system.

In the case of reinforced concrete tunnels, the material properties of the part can first be determined under the influence of temperature. In addition to concrete, as well as steel, the characteristics during the fire and the residual strength after the fire are determined. As a precondition for this, the internal reinforcement must be protected accordingly. If internal rebar exposed to heat is not protected from overheating, not only residual strength but also support performance is not maintained. The rebar can only be protected by a cover of relatively large size. In this case it is very important to prevent flaking of the cover by reinforcing the skin or adding polypropylene fibers.

According to the temperature (T) of the cross section given through the temperature gradient at each time point (t), different material properties are generated for each part of the cross section. Therefore, the effective modulus of elasticity (D-Modul) at each point of the cross section is

Em = f (T (f (t)))

The modulus of elasticity represents the function of temperature, and the function of temperature again represents the function of time. This is the strength of the effective concrete or steel respectively

sigma, m = f (T (f (t)))

The same applies to the case.

These material properties, which continue to differ across the cross section, are now integrated above the cross section height, resulting in the overall properties of the cross section with a dominant temperature load at this point.

Individual cross-sectional properties for predefined limit extension states are integrated using a computer program, and each possible supporting load is calculated. The cover is formed through the deformation of the edge extension, resulting in a support load curve.

As is often the case in reinforced concrete-supported load curves, the supporting capacity of the individual cross sections depends on the definition of the limit elongation, in particular in which an increase in the allowable concrete compression plays a significant role. The definition of limit elongation affects especially when the cross section is subjected to temperature loads.

As expected, the temperature loads reduce the overall cross-sectional support performance and at the same time show the asymmetric supporting behaviour of the cross section, because for geometrically symmetric cross sections the material properties themselves are asymmetric. As can be seen, the maximum allowable concrete compaction increases the support capacity of the cross section significantly. This is because no higher and effective concrete tension can occur at the edges at all, but in slightly lower cross-sectional areas, larger load reserves can be carried out when the concrete compression is higher.

As with the supporting load of the cross section, as the temperature load increases gradually, the stiffness of the cross section, which is caused by the continuous decrease of the height of the cross section due to the overload due to temperature, on the one hand, is also reduced. . This is because all cross-sectional parts disappear at a temperature load of 700 ° C.

As with the calculation of the supporting load, it is desirable to calculate the quotient for the stiffness of the entire cross section through the definition of the elastic modulus effective at each site of the cross section.

As already mentioned, this method will suffice for linear support statics. To ensure this, the temperature load in the cross section must be changed.

In linear support statics only linear trends of temperature gradients are allowed. As can be seen, the actual temperature gradient is quite different from the linear trend. As such, the edge zones are generally heavily loaded with temperature, and the cross-section portions that continue to be located inside and the cross-section portions that escape the fire are generally subjected to little or no temperature load.

Similarly, reduced material properties are only important in areas with increased temperature loads, and the original material properties still apply to the remaining cross sections.

Similar to the calculation of the supporting load, the internal stress state can be defined for each temperature load, which is determined by the temperature prevailing and the dominant temperature on the one hand at each site, respectively. On the other hand, at each point the material properties can be defined according to the temperature, so that the total load can be calculated from a predetermined temperature gradient.

These internal cutting forces can be converted back to equivalent external temperature loads in the next step, respectively, because of these external temperature loads the stress states are not the same but the internal cross section sizes are the same.

As such the magnitude of the temperature load is equal, the cross-sectional size can be calculated using linear support statics, and the results of the linear support statics based on bending moments and normal forces clearly show the support load curves. Are distinguished.

All the prerequisites for carrying out the supporting load proof are prepared with the calculation steps listed above. Equivalent temperature loads are added to the working loads even if they are not, and the cross-sectional size is calculated using linear support statics. The interaction of these cross-sectional sizes is clearly distinguished from the support load curve of each cross section, thereby demonstrating the support stability.

If the proven system is still required to remain stable after the fire until the corresponding reconstruction measures are taken, the supporting stability after the fire should also be demonstrated.

In the case of material properties correspondingly reduced by fire load, this should be done in the case of steel as well as concrete. This should be taken into account when securing the required rebars, first of all to allow the section size to be calculated in structures with no fire load but varying stiffness ratios. Only then can the measurement be verified with reduced material properties, where the required stability factor must be set.

The invention is described in detail with reference to the accompanying drawings in the following, on the basis of examples.

1 is a chart showing temperature trends in the cross section of a part over time.

FIG. 2 is a diagram schematically showing the transition of cutting forces appearing in the tunnel cross section when a fire is started.

3 is a diagram showing the diagram of FIG. 2 after 180 minutes have elapsed after a fire has occurred.

FIG. 4 is a diagram showing that a bending moment is applied above normal force. FIG.

5 is a system diagram showing the progress of the method according to the invention.

A general tunnel cross section with elastic insertion is shown, the size of which is as follows.

Internal sheet cross section = 40 cm

Rebar inside, outside = 5 ㎠ / m

Concrete quality B300

Steel quality ST 55

Ballast modulus 100,000 kN / ㎡

6 m inside diameter

Superposition = 10 m light soil

2 m under water level GOK

Outside the concrete cover = 5 cm

Inside concrete cover = 10 cm

Inside protective rebar, d = 3 cm (used to limit peeling under the influence of temperature)

Fire loads are always established around the tunnel cross section. The longer the duration of the fire, the deeper the temperature load penetrates into the cross section.

1 shows temperature trends over time in parts such as tunnel walls, for example. The distance from the exposed surface is presented in centimeters on the horizontal axis. The degrees Celsius is shown on the vertical axis, and the individual curves are 3 minutes, 6 minutes, 9 minutes, 30 minutes, 60 minutes, 120 minutes to 180 minutes since the exposure began. Indicates a later temperature change.

From load types such as dead load, earth pressure and water load, cross-sectional sizes with minimum reinforcement are created. 2 shows the cutting force trend in the tunnel profile at time t = 0, ie before the load caused by the fire begins.

The similar diagram in FIG. 3 shows the cutting force 180 minutes after the fire, with the cross sectional sizes overlapping due to the temperature load.

It is possible to anticipate a continuous increase in vertical force in the system after calculating different time points t, but the vertical force weakens with longer fire durations and depends on the stiffness of the ballast.

In contrast, the moment load first rises tremendously in the cross section, and then drops correspondingly sharply again after reaching a maximum. This is because the internal load at the start of the fire is very eccentric due to the temperature gradient, but after some degree of fire, the temperature load is still increasing but the eccentricity is quite low.

Support stability is demonstrated by the corresponding support load curve. The example presented shows that the cross section also still has a support stability of at least one (> 1) after 180 minutes of fire load.

4 shows a diagram in which the vertical force is applied at kN on the horizontal axis and the bending moment is applied at kNm on the vertical axis.

This demonstrates that, in the event of a fire, the stability of cross sections with at least one stability without further action is ensured.

In addition to the steps presented, it is necessary to exclude cross-sectional areas where the temperature load is 700 ° C or higher during the calculation. This corresponds to the specified material properties.

The computational model according to the present invention is based on the strength of materials and reinforced concrete structures without the use of complex figures, and can be used to demonstrate the support stability of a support system under fire load using linear support statics. have.

The system diagram of Fig. 5 shows the calculation process of the model according to the invention. Beginning with defining the fire load in step 1, the temperature load in the cross section is calculated in step 2, and in step 3 the calculation of the time step ti is carried out. Step 4 then calculates all time steps, in order to be able to define the state after the fire in step 5. From this, in step 6 the requirements for the structure can be derived.

In detail, step 3 can be viewed as a subprogram, where the stiffness of the system is determined in step 31 of the loop, and the temperature and equivalent load in step 32. This results in the calculation of the support stress in step 33, the measurement of the components in step 34 and the test of the support performance in step 35. If verified, the program returns, and if not verified, step 31 returns.

For these calculation models, the support load calculation step, which is largely excluded in the design, can be included effortlessly and the effects of measures such as insulation and other structural measures can be investigated. This eliminates the purely empirical arrangement of these measures. Also, as an alternative to the principle arrangement of insulation in the form of mats and plaster or protective concrete, a scheme can be proposed to adhere only to the principles of reinforced reinforced concrete support structures.

The present invention can be calculated without the use of complex numerical calculation methods by developing a calculation method, and has the effect of demonstrating the support stability of a statically loaded concrete building during and after a fire.

Claims (4)

It relates to the design of parts that already exist in the structure of the part and that are suitable for standard load types such as dead weight, water load, pressure of earth, and working load. Based on the data obtained using the), the supporting stability of the supporting system under fire load is calculated by calculating changes in material properties and residual strength after the fire. As a way to prove it, For parts affected by temperature, the input value for calculation, Defining the fire load, Determining the arbitrary time point t and calculating the temperature load across the cross section at said time point t, Determining material properties under temperature and fire effects Is determined through Using the data determined over the cross section height of the part at each time step, taking into account the different nonlinear material properties that appear in each section of the cross section by being incorporated within the defined limit extension state, Calculating the supporting performance of the cross section through the interaction of bending moment and normal force using a supporting load curve for the cross section at that time, ie a supporting load curve step, Converting the internal cutting force due to the temperature load when the external temperature load is equivalent, and Calculating the stiffness and bending stiffness defined in the system stiffness that are commonly used in the considered cross sections. Characterized in that it is possible to clearly distinguish the cross-sectional sizes obtained by using a stabilizing tension calculation from the next commonly used supporting load curve while taking into account the changed stiffness and the equivalent temperature load applied. How to demonstrate supportive stability. In claim 1, The method of claim 1, wherein the method of demonstrating support stability has varied material properties that can be determined and is repeated for a long time until a desired support stability is reached, when the support stability of the support system is negatively verified. In claim 2, Wherein the material properties can be changed by increasing the amount of rebar and / or by increasing the concrete content and / or by including the flow link in the calculation. In the case of a fire that may occur after a design to build a static load-bearing structure, the supporting stability of the structure is derived from the part structure itself and is related to the design of parts suitable for standard load types such as dead load, water load, earth pressure and dynamic load. And calculated based on the data obtained using support statics, and in some cases, the characteristics of the structure can be changed to the extent that the supporting stability at the time of fire load or the required residual strength after the fire is given. Use of a method of demonstrating supportive stability according to any of the preceding claims.