CN102677708A - Method for applying prestress by reaction beam for static load test of pile foundation and steel box girder - Google Patents

Abstract

The invention discloses a method for applying a prestress by a reaction beam for a static load test of a pile foundation and a steel box girder, and is characterized in that a steel pipe is buried in the steel box girder, multiple steel strands penetrate through the steel pipe, the steel strands on two ends of the steel box girder are respectively provided with a ground tackle used for locking and fixing the steel strands, and both ends of the steel strands are tensed by a tension jack, so that the steel box girder generates the prestress. Through tensing the prestress steel strands, the steel strands stretch to reach a control stress and are released. In a release process, the prestress steel strands are locked by the prestress ground tackle, so that a section of the steel box girder bears an inner pressure, thus the crack resistance and the deformation performance of a structure are improved, at this time, the pull stress of the prestress steel strands and the pressure stress in the steel box girder form a self-balance system. The bearing capacity of the steel box girder is improved without increasing steel materials, and the bearing capacity under a unit weight is improved; the intensity of the steel box girder meets requirements of a large-tonnage static load test; the steel material is saved, and the cost is reduced.

Description

The test of static load of pile foundation lotus applies prestressed method and steel case beam with reaction beam

Technical field

The present invention discloses a kind of static load of pile foundation lotus test and applies prestressed method with reaction beam, also provides simultaneously to have applied steel box girder with prestressed tendons, belongs to constructional materials detection technique field.

Background technology

The used reaction beam of static load of pile foundation lotus test was common steel case beam in the past, was characterized in Heavy Weight, particularly when doing the large-tonnage static loading test, needed hoister in large tonnage to install.Meet more large-tonnage static loading test on occasion, the intensity of existing steel case beam has satisfied not test requirements document.This just needs to make bigger steel case beam could accomplish test mission.

Summary of the invention

The present invention discloses a kind of static load of pile foundation lotus test and applies prestressed method with reaction beam, has solved the used reaction beam of conventional static load of pile foundation lotus test and has done the large-tonnage static loading test, and the intensity of steel case beam has satisfied not the problem of test requirements document.

The present invention also further provides the steel box girder with prestressed tendons that realizes said method, can satisfy the test of static load of pile foundation lotus.

Static load of pile foundation lotus test of the present invention applies prestressed method with reaction beam, adopts following technical solution:

In steel case beam, be embedded with steel pipe, wear some steel strand in the steel pipe, it is fixing with the steel strand pinning that a ground tackle respectively is set on the steel strand of steel case beam two ends, connects through stretch-draw jack pair steel strand two ends and carry out stretch-draw, makes steel case beam produce prestressing force.

A kind of static load of pile foundation lotus test of the present invention is with applying steel box girder with prestressed tendons, and its structure is following:

In steel case beam, be embedded with steel pipe, wear some steel strand in the steel pipe, be marked with cement paste in the steel pipe steel strand are wrapped up, a ground tackle respectively is set on the steel strand of steel case beam two ends steel strand is pinned fixing.

Inject cement paste in the steel pipe, prestress wire is encased with cement paste fully, make prestress wire can not produce corrosion, brush rustproof paint with around the ground tackle simultaneously, and with on the jacket casing, to strengthen the protection to ground tackle.

Below calculate and show good effect of the present invention:

1, applies prestressing force stage and calculating

In steel case beam, applying prestressing force, mainly is to make the cross section of originally bearing pulling force, applies a pressure to it earlier; Compressive stress is born in the cross section of then exerting pressure; Below neutral axis, bear tensile stress, apply prestressing force stage sketch map and see Fig. 3 for details, its section stress figure is seen Fig. 4; Wherein, A _yIt is the presstressed reinforcing steel area; σ _KonIt is control stress for prestressing.

The additional bending moment that produces when 2, calculating prestressed stretch-draw

Referring to Fig. 5, when applying prestressing force for steel case beam, be exactly an eccentric compression member as far as steel case beam, then make the additional bending moment of steel case beam generation be because of applying prestressing force:

M=e _0?A _yσ _kon=400×137.41×14×1860×0.75=1073kN·m

Moment M=the 1073kNm that under the prestressing force effect, produces;

3, operational phase

Steel case beam operational phase loading process is referring to Fig. 6 and Fig. 7:

Operational phase steel case beam top its section stress of portion's pressurized of being left behind is seen Fig. 7 section when power P reaches a certain numerical value, and the compressive stress that beam top produces in the time of just overcoming prestressed stretch-draw is obtained the P value, promptly is the bearing capacity that is improved behind the prestressing force by applying.With the test span is that 6m calculates

M=

P L

In the formula: the M--moment of flexure (additional bending moment that is produced after being equivalent to apply prestressing force) that steel case beam produces under power P effect

The P--trial load

L-steel case beam span

P _{In advance}=

KN

Can know through aforementioned calculation, through applying the trial load that this steel case beam of prestressing force can improve 715kN.

4, the bearing capacity calculation of steel case beam itself

Steel case beam moment of inertia I= =5646826667mm ⁴

Bending resistant section coefficient ω=

=12014524mm ³

σ= (using 16 manganese steel plates to make design strength 310MPa)

M=σω=310×12014524=3725kN·M

P _Steel=

KN

Overall test load P _Always=P _{In advance}+ P _Steel=715+2483=3198kN

Can improve bearing capacity 715/2483=28.8%

5, analyze relatively

Heavy (0.38 * 6+0.9 * 6) * 0.02 * 2 * 7.85=2.41 of steel case beam ^T

Prestress wire weighs 11.01 * 6.5 * 14=1kN

Apply the preceding Unit Weight bearing capacity

of prestressing force=103 kN/kN

Apply Unit Weight bearing capacity

=127 kN/kN behind the prestressing force

The Unit Weight bearing capacity improves 127-103=24kN/kN

Improve 24/103=23.3%

6, conclusion

Apply through aforementioned calculation that bearing capacity improves 28.8% behind the prestressing force; Unit Weight steel bearing capacity improves 23.3%.Promptly improved bearing capacity, also having practiced thrift steel is the testing equipments that are worthy to be popularized.

Be at good effect of the present invention:Making it elongation through the stretch-draw prestressing force steel strand puts after reaching proof stress and opens.In putting a process; Through prestressed anchor prestress wire is pinned, makes steel case beam section receive internal pressure; Thereby improve the cracking resistance and the deformation performance of structure, the compressive stress during this in tensile stress of prestress wire and the steel case beam is formed a self-balancing system.Apply that steel strand intensity is 1860MPa behind the prestressing force; It is common

level 5.5 times of steel; Therefore; Under the situation that does not increase steel, improve the bearing capacity of steel case beam, improve the bearing capacity under the Unit Weight; The intensity of steel case beam has satisfied the requirement of large-tonnage static loading test; Also just be equivalent to practice thrift steel, reduced cost.

Description of drawings

Fig. 1 is a structure principle chart of the present invention;

Fig. 2 is a cross section structure schematic diagram of the present invention;

Fig. 3 applies the prestressing force stage diagram for steel case beam;

Fig. 4 applies prestressing force section stress figure for steel case beam;

Fig. 5 is a steel case beam eccentric compression calculating chart;

Fig. 6 is a steel case beam operational phase force diagram;

Fig. 7 is steel case beam operational phase section stress figure.

The specific embodiment

Embodiment 1

Like Fig. 1, shown in Figure 2; Steel case beam 1 is of a size of 9500 * 380 * 940mm, and steel case beam 1 an interior steel pipe 2 is worn 14 φ, 15 steel strand 3 in steel pipe 2; Crowd's anchor ground tackle 4 in one 14 hole respectively is set in steel strand 3 terminations; And pin with the anchor sheet, carry out stretch-draw with the stretch-draw jack then, the control stress for prestressing of every steel strand 3 be (referring to Fig. 3 ~ Fig. 7):

σ _kon=0.75f _ptk=0.75×1860=1395M _Pa

Every steel twisted-line tension-force P _Single=1395 * 137.41=191kN

14 total stretching force P _Always=191 * 14=2674 kN

In the formula: σ _Kon-control stress for prestressing is got σ _Kon=0.75 f _Ptk

f _Ptk-prestress wire strength standard value (is 1860 M _Pa)

137.41 the section area of-steel strand.

For increasing the durability of prestress wire, cement injection in the steel pipe 2 encases prestress wire 3 fully with cement paste; Make prestress wire 3 can not produce corrosion; Simultaneously ground tackle 4 is brushed rustproof paint on every side, and with on the jacket casing, to strengthen the protection to ground tackle.

Do secondary beam with above 8 steel box girder with prestressed tendons, do girder, realized that the maximum at present trial load of our province is the static load test of 22000kN with original 4 steel case beams.

Claims (2)

1. a static load of pile foundation lotus test applies prestressed method with reaction beam, may further comprise the steps:

In steel case beam, be embedded with steel pipe, wear some steel strand in the steel pipe, it is fixing with the steel strand pinning that a ground tackle respectively is set on the steel strand of steel case beam two ends, connects through stretch-draw jack pair steel strand two ends and carry out stretch-draw, makes steel case beam produce prestressing force.

2. a static load of pile foundation lotus test is with applying prestressed steel girder, and its structure is following:

In steel case beam, be embedded with steel pipe, wear some steel strand in the steel pipe, be marked with cement paste in the steel pipe steel strand are wrapped up, a ground tackle respectively is set on the steel strand of steel case beam two ends steel strand is pinned fixing.

Images