Tai Po Liu External Prestressing reinforcement bri

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Liu Tai Po bridge design prestressing reinforcement

Abstract: Great Bridge in Tianjin Baodi Liu Po Kowloon Park County on the road in Chaobai. Bridge length of 790.3 meters, the bridge deck width 9 m (ie 1 +7 +1), the upper structure 56 holes, five span of 14.1 meters of reinforced concrete T-Beam bridge, there are three transverse cross to partition. Reinforced concrete pavement (7.5 ~ 11 ~ 7.5 cm) and 3 cm asphalt concrete surface layer. Each hole is an expansion joint 8, during a continuous pavement for the bridge.
Keywords: External Prestressing T beam bridge

Great Bridge in Tianjin Baodi Liu Po Kowloon Park County on the road in Chaobai. Bridge length of 790.3 meters, the bridge deck width 9 m (ie 1 +7 +1), the upper structure 56 holes, five span of 14.1 meters of reinforced concrete T-Beam bridge, there are three transverse cross to partition. Reinforced concrete pavement (7.5 ~ 11 ~ 7.5 cm) and 3 cm asphalt concrete surface layer. Each hole is an expansion joint 8, during a continuous pavement for the bridge. Old T-beam shape (Figure 1). Old beam design load rating: steam -13, -60 drag. Substructure piers and capping beam is in the original bridge site on the upstream side of the 95 re-designed and built for a single row of double-pile (pillar), the load rating: steam -20, hanging -100. Commissioned by the Road Development Corporation, our hospital on April 12 ~ 13, the bridge was examined. Since the old low-road technical standards (steam -13, -60 drag), passing ability, coupled with the current increase in traffic volume and vehicle load increases, the old bridge can not meet the capacity requirements. By funding and material resources and diplomatic relations to time constraints, can not all removed and new, can only consider investing in small, short duration and can increase the capacity of technology to transform a variety of bridge reinforcement. Which uses external prestressing steel processing technology, and can do as a simple structure with the new lower loads (steam -20, hanging -100) in line with the effective way. External Prestressing method is based on the substance of crude steel, steel cable or high-strength steel and other steel products as a force tool, applied externally prestressed bridge superstructure, with its resulting offset part of the anti external load produced bending moment internal forces, so as to improve its performance using the old bridge and improve the bearing capacity of the end, the bridge involves only crude steel External Prestressing increased load programs.
One prestressing structure: mainly consists of four parts
1, the level of tendon and oblique muscle: from high-strength steel coarse threaded components, structure shown in Figure 2, whose role is to improve the prestressed beams.
2, Beam Anchor: first beam cutting away part of the concrete bridge deck, the top surface of the beam and oblique muscle hewn tilt angle perpendicular to the direction of the slope (to be cut locally erect steel and stirrups), cut in the side on the diaphragm muscle in the same direction and oblique slant-hole, and then use the angle or the channel will support the production of a fixed pedestal with epoxy mortar has been drilled in a good slant on the beam. Oblique tendon through the horizontal beam and the slant-hole bearing pedestal, with the jack and nut for tensioning anchor seat in the bearings, and finally closed with concrete anchor head, shown in Figure 3.
3, horizontal sliders: oblique muscle by the Center's activities and level of reinforcement and fixed in the slider bearing in the supporting steel beam bottom pad composition, its structure shown in Figure 4, whose main function is to slide through the level of the slider, to adjust the level of oblique muscle tendon with the ratio between the internal forces and make the force more uniform surface.
Second, the external prestressing to improve load rating calculations: known design parameters are as follows:
1. T beam concrete design label 25Mpa. Calculation of tendon ultimate stress level, take , when the cross-section strength calculation design strength of concrete in compression to take , to take concrete ultimate compressive strain
2. The original T beam reinforcement parameters: the T beam reinforcement shown in Figure 5
Span section: ,

Fulcrum section: ,
, ,
. The original beams in the longitudinal tensile steel reinforcement ratio :

3. External tendon reinforcement parameters:
, Reinforced design and analysis, in vitro muscle is taken as the level cable , oblique muscle is taken as , are cold-drawn steel grade Ⅲ (single controller).

Two horizontal distance between the plate center: , the anchor point to the horizontal distance between the center plate:
,
T beams externally prestressed tendons to the end of the distance

Prestressing loss:
1) the level of prestressing steel and the friction between the slider : is the level of tension due to
2) with a deformation caused by loss of prestress : , due to the level of tension is, therefore , check specifications by total,

3) temperature difference caused by the loss of : .
, : prestressed steel bars and concrete are the linear expansion coefficient ,
, Δt: for the construction of the annual maximum temperature and the temperature difference; 15 °
It:
4) batches of concrete tension caused by elastic compression loss : two levels for single beam tension steel at the same time, the single beam between the .
5) steel relaxation losses caused : a tension
6) concrete shrinkage and creep stress caused by the loss
Old bridge due to concrete shrinkage and creep in the long process has been completed. Reinforcement bars in vitro system does not make a lot of bridges to increase the dead load, and the beam compression zone so that the original stress decreased significantly. Therefore,[link widoczny dla zalogowanych], you can take concrete approximate shrinkage and creep losses . Thus, in vitro reinforcement of prestressed tendons total stress loss:
Prestress level focus to the cross section bar from the edge of
Unbonded prestressed tendons effective , the slider and the coefficient of friction between the beam bottom (of the sliding friction) , reflecting the level of oblique muscle and tendon The ratio of the coefficient of tension , external oblique muscle in the effective prestress
1, calculate the ultimate stress of steel in vitro:
Oblique muscle tendons and the level of material and its cross-sectional area at the differences, the effective prestress is different, which is also different between the two dependent variables. Prevail if the level of tendon strain, the strain state of the oblique muscle converted to the strain state of horizontal bar, and obtained in this case the total length of tendon in vitro, that is, the conversion length of tendon in vitro. Where , respectively, in vitro and oblique muscle tendon prestress level in the strain produced by the effective prestress.
, the . Order: . Beam cross section in the stiffness and ultimate destruction of the state of the beam cross-section ratio of the average stiffness , in vitro translation of prestressed reinforcement calculation of the beam span length of , and supporting conditions of the deflection coefficient for consideration by uniform load by the elastic deformation of simple beam theory can be obtained , the level of reinforcement ratio in vitro , the original beam tension reinforcement ratio , the original beam compression reinforcement ratio , with reference to the existing Highway Bridge Specifications (JTJ023-85) in reinforced concrete and prestressed Strength Concrete Beams calculation method, calculated by the rectangular cross-sectional interview: the ultimate stress of tendon in vitro level , R a b ' i χ = σ A y + A g R g - A ' g R ' g is , so that the level of Limit bar high coefficient ξ y cross section for the Liang Fasheng the actual depth of compression zone at failure χ s and in vitro to the beam center of gravity horizontal bar of the distance between the top surface ratio, which ,
∴ , then substituted into the above equation, we obtain , and with this type expand order that was the limit of horizontal bar of rectangular cross-section in vitro high coefficient , levels of in vitro tendon ultimate stress increment, the above formula

Assumed in Figure 6 occurs when the damaged section of maximum bending moment, the two beams are not damaged section of rigid rotation occurred, that is, without the geometric relationship between deflection, similar to the triangle than the geometric equations can be established as follows: ; : the total prestressing steel elongation. : beam damage to the limit when the deflection value. : Liang Fasheng section failure when the actual depth of compression zone. From the above we obtain: , based on the total elongation to find the ultimate strain of prestressing steel incremental ; consider the effective prestressing tendons in vitro the effect of in vitro tendon strain the limits of where ε y to the level of external prestressing tendons produced by the effective prestress strain. As the level of muscle in vitro in the beam reaches the yield limit state is not, therefore, the above equation by multiplying both ends of the elastic modulus of prestressed reinforcement, the ultimate stress of tendon in vitro levels can be expressed as: This type is the second level of external prestressing tendon ultimate stress increment , and because and the ultimate deflection of reinforced concrete beams span is can be derived: to obtain a simplified limit on the level of tendon stress increment of a quadratic equation. Namely: ; where coefficient

Solving equations: : ie: ;
Solved:: ; the level of muscle stress limit:

Oblique muscle in vitro ultimate stress formula: ; external oblique muscle and the level of the reinforcement area is different from whichever is greater, ; the

2. Calculation of the bending strength
The <
, that the neutral axis within the T beam roof, is the first T-shaped. Thus according to a width of bending strength of rectangular cross section. This can be ignored in the reinforcement of the compression zone, calculated from the neutral axis position specifications:
Tension reinforcement The point of the level of muscle tendons from the center of gravity is:
;

Further reinforced by the standardized formula to calculate the flexural strength system:

The beam after the vehicle load to improve grade control design, the maximum cross-section calculation in the bending moment ;
Therefore, in vitro reinforcement bars , the beam flexural strength to meet the design.
3. Calculation of shear strength
Fulcrum of the beam shear largest -100 control by the trailer, its value is ; role in the end beam prestressing force in tendons in vitro should be considered as an external force, which will offset part of the vertical component outside the shear load. Assume that in the limit state, the oblique muscle in vitro stress , consider the material safety factor, then the pre-shear of the vertical component is: ;
;
; calculations show that the back rest side by in vitro reinforcement bars do not appear inclined compression failure.
By the specification (4.1.10-2) and (4.1.10-3), we have:

Reinforced tendons in vitro, the beam shear strength to meet the requirements.