Construction of prestressed zhangfazhangla
after
1 scope
This technology is applicable to general
industrial and civil construction post-tensioned prestressed concrete in
hydraulic construction (does not include components and systems).
2 construction preparation
2.1 materials and equipment
2.1.1 prestressing tendon: heat treatment
of steel, for Prestressed steel wire, steel wire diameter of the varieties,
specifications, and must comply with the design requirements and national standards,
certificates of quality should be tried again and reports. Cold drawn ⅰ, ⅱ, ⅲ steel bars
should also be drawn after the mechanical performance test report.
2.1.2 prestressed anchorage, fixtures and
connectors in the form of, should comply with the design requirements and
technical specification for, factory certificate, to enter the construction
site shall be in accordance with the code for construction and acceptance of
concrete structures (GB50204-92) of static load test for acceptance and assemblies.
2.1.3 Grouting with cement shall not be
lower than No. 425, Portland cement, or according to the design requirements,
certificate and retest report of the factory.
2.1.4 main equipment: hydraulic tensile
machine, electric fuel pump, filling machines, mold testing, etc.
2.2 operating conditions
2.2.1 prestressed stretching machine has
been verified and documented. Commissioning check the stretch wrap machinery
and equipment and reliable, if there are any exceptions should be repaired
before use. Grouting equipment ready to go.
2.2.2 concrete elements (or blocks) must
meet the design requirements of strength, such as when there is no requirement,
should not be lower than the design strength of the 75%. Widget (or block) of
several sizes, appearance, quality, obligate and the pipe shall be subject to
inspection and acceptance of qualified and finished assembling the blocks have
to be assembled and inspected.
2.2.3 anchor clamps, connector should be
prepared, and after checking.
2.2.4 prestressing tendon or tendon has
been completed.
2.2.5 Grouting cement paste (or mortar) mix
and end-concrete mix proportion test OK.
2.2.6 stretching space should be smooth and
unobstructed, tension at both ends of the safety precautions.
2.2.7 has been technology gives the low-down
and tensioning of prestressed tendons of tonnage should be with the
corresponding gauge readings, steel bar calculating elongation value written on
the cards, and hung in the clear position, so that when you observe master.
3 operational processes
3.1 process:
Check widget (or block)
↓
Tendons make → wear prestressed
tendons
↓
Anchor test → installation and
tensioning equipment check tensioning equipment
↓
Tensioning
↓
→ Making of duct Grouting cement blocks
↓
← Lifting cement blocks
3.2 check the widget (or block): carefully
check for prestressing duct. Must ensure that the size of the duct and position
correctly, ride smooth, without local curvature embedded steel plates duct ends
should be perpendicular to the axis of the channel, duct joints must not leak
slurry, filling holes and vents shall conform to the design requirements of the
position. When the channel does not meet the requirements, or to clean up as
well.
3.3 wear prestressed reinforcement.
3.3.1 before the wear bars, bars should be
checked (or bundle) specification specification, with a total length of.
3.3.2 wear when reinforced, prestressed
reinforcement with a Swiss screw, thread should be protected to avoid damage.
Steel beams or steel wire beams steel or wire should be sequentially numbered
and put on beam. First or reinforced the wire from one end of the beam
penetrating into the pores, at the other end wore out, then gradually pull the
steel bars or steel beam to the other side.
3.3.3 reinforced wear will beam in Member
State, so as to check against.
3.4 install anchorages and tensioning
devices: installation of anchorages and tensioning devices, linear tendons
should be pulled from the line and hole center line overlap in the stretching
process; of curved prestressed reinforcement should be pulled from the line
coincides with the center of duct end tangents.
3.5:
3.5.1 prestress stretching program should
be carried out according to the design, if the design is provided, you can take
one of the following programs:
3.5.1.1 0 105% con Lotus 2min → σ → σ con.
3.5.1.2 0→103%σcon
Σ con for the prestress of tensioned control stress.
3.5.2 the tension order of prestressed
reinforcement shall conform to the design requirements, when no specific design
requirements, partial, phased symmetric stretching can be done.
Partial tension, you should calculate the
prestressing loss value of partial tension, were added to the pretensioning
prestressing tendon tensioned control stress values, or use the same pull
values reset make up one by one.
3.5.3 single prestressed reinforcing rebar
(stretcher tensioning screws-side anchor) tension, should be a little strength,
pad location according to the design requirements, and then press the
tensioning procedure prescribed tension. Stretching is completed, tighten the
nuts boards, anchorage, reinforced actual elongation value is measured and made
tension records.
3.5.4 tendon using double-acting jacks
tensioning tapered anchors when the last anchor, should operate according to
the following requirements:
3.5.4.1: pulling a short length of wire,
check the length of each wire to reach agreement, if inconsistent, should
adjust back wedge, then tight wedges.
3.5.4.2 tension and pressure: pull
tensioning procedure prescribed tension can be adjusted to the rear. Tensioning
is complete, measure the elongation value of steel wire, suffering in
accordance with provisions, top anchor can be carried out. Top pressure
cylinder hydraulic circuit must be turned off when the anchor plug, small
cylinder oil, let the small cylinder piston top anchor.
3.5.4.3 check: mount the Jack is not
stretching tension at one end, after stretching to control stress, and anchor.
When tensioning pressure is finished, slide wire into specification of neck-in
anchor last, if larger than regulation value, must be tensioned again, make up
for the loss.
3.5.4.4 the number of broken wires in wire
and slip, the same section of no more than 3% of all wire, and a bunch of wires
allowed only one. If it exceeds the above provisions must be tensioned,
tensioning wire to the original tonnage, Larsson anchor plug with a steel
insert padding notches in the stuck bolt and cylinder oil, anchor plug was
pulled out, remove the entire anchor last. Check whether the anchor ring is
individually cut grooves, anchor plug is pumped with fine teeth, if there are
such cases, to change the anchor back tension if the anchor ring, anchor plug
is still intact, as long as the top pressure increase the pressure pushing
anchor plugs.
3.6 complete prestressed records.
3.7 duct Grouting:
3.7.1 grouted ducts should be pressurized
water clean and check that the filling holes, vent prestressed duct connected,
otherwise, should be dealt with in advance.
3.7.2 tendons pull out as soon as possible
after Grouting to reduce losses.
3.7.3 grout pressure is generally
0.4~0.6MPa.
3.7.4 filling sequence should be on the
lower rear, avoiding the upper duct leakage channels through lower, after
treating the vent emitting thick, blocked vent and pressure Grouting to 0.6MPa,
keep after l~2min, you can plug the hole.
3.7.5 making blocks and pay attention to
conservation.
Capped 3.8 pouring concrete or end
treatment, and maintenance;
4 quality criteria
4.1 project:
4.1.1 prestressing variety and quality must
comply with the design requirements and the provisions of the relevant
standard.
Inspection method: quality inspection
certificate and test report.
4.1.2 mechanical properties of cold-drawn
steel must comply with the design requirements and the provisions of the code.
Inspection method: quality inspection
certificates, test reports and drawn record.
4.1.3 prestressing of anchor equipment,
fixtures and quality of connectors must comply with the design requirements and
specifications and special provisions.
Check number: code for construction and
acceptance of concrete structures according to the sixth chapter 6th. Article
2.12 extract specimens.
Inspection method: check the anchors,
clamps and connector factory certificate of static load anchoring performance
and appearance, hardness, dimensional check report.
4.1.4 the strength of concrete and concrete
block vertical seam (mortar), strength, design and construction norms and
regulations must be met.
Inspection method: check the same condition
curing concrete (mortar) sample test report.
4.1.5 anchoring phases stretching tendons
in end of neck-in must conform to the specification for concrete construction
6th. provisions of article 3.9.
Inspection method: examination of
prestressing records.
4.1.6 channel must comply with the
requirements or specifications of cement strength requirement.
Inspection method: careful observation of
inspection and check of cement test block test report.
4.2 Basic project:
4.2.1 the actual establishment of prestress
design percentage of deviation shall not exceed ± 5%.
Check the number: press the spot check of
the number of different types of prestressed concrete 10%, but shall not be
less than 3.
Inspection method: examination of
prestressing records.
4.2.2 prestressed reinforcement (steel
wire, steel wire or steel) breakage or slippage is strictly prohibited in the
number over the same section of prestressed 3% of the total number, not more
than one and a bunch of wires.
Check amount: total inspection.
Inspection method: comprehensive
observation and inspection of prestressing records.
5 finished product protection
5.1 members shall not be distorted and
corrupted when lifting.
5.2 piling yard should be smooth, solid and
pad from top to bottom.
6 quality problems to be noticed
6.1 setting on the tensioning side, should
comply with the design requirements, when no specific design requirements,
shall comply with the following requirements:
6.1.1 core forming hole tensioning: the
curve prestressing tendons in line and length is greater than 24m should be in
tension on both ends; the line length is not more than 24m prestressing tendons
can be tensioned.
6.1.2 when embedded corrugated pipe ducts
prestressing: curve prestressing tendons in line and length is greater than 30m
should be tensioned at the ends, the line length is not more than 30m
prestressing tendons can be tensioned.
When the same section when there are
multiple tensioned tendons, tension-side should be set at the ends of the
structure.
When tensioning prestressed reinforcement
at the same time, anchoring one end first, and then make up the tension at the
other end after the anchor.
6.2 horizontal overlap placement of
components, on the first layer under tension. For reducing the prestress loss
due to friction between the upper and lower layers, layer-by-layer to increase
tension. But bottom Zhang pull should not be than top layer Zhang pull big 5%
(wire, and steel twisted line, and heat treatment steel) or 9% (cold drawn II,
and III, and IV level steel), and maximum tension stress: cold pulled II, and
III, and IV level steel shall not over yield strength of 90%, wire, and steel
twisted line shall not over yield strength of 75%, heat treatment steel shall
not over standard strength of 70%. After tensioning the actual prestressing
deviation must not exceed the specified value 5%.
6.3 anchor after the exposure length, of
not less than 30mm. Capped concrete anchor applications protection, such as
long term exposure, measures should be taken to prevent corrosion.
6.4 after the prestressing, hole filling as
soon as possible. Connectors for connection of multi-span prestressed duct
Grouting should be immediately pulled out a pouring across should not span all
the tension after the completion of a continuous filling.
6.5 marking of duct Grouting should be
adopted no less than No. 425 of ordinary Portland Cement Grout that is
configured; pore channel mortar grout can be used. Cement and mortar, shall
meet the design requirements, both of which should not be less than 20N/mm2.
6.6-filling cement slurry cement 0.4~0.45,
3h bleeding rate after mixing should be controlled in the 2%, the maximum shall
not exceed 3%, can be added into cement admixture of prestressed reinforcement
corrosion-free. Can be mixed with 0.05%~0.1% aluminium powder or calcium
lignosulphonate water-reducing agent of 0.25%.
6.7 when cold-drawn thick reinforced bar
for prestressing tendons, must weld rod screws at the top, and then cold-drawn,
all welding a cold drop test.
7 quality records
This standard shall meet the following
quality records:
7.1 components, concrete blocks stretching
strength of test piece test report form.
7.2 quality prestressing certificate or
test report form.
7.3 the cold-drawn prestressed tendons
records.
7.4 experimental report on mechanical
properties of cold-drawn prestressed reinforcement.
7.5 welded joints of cold-drawn prestressed
reinforcement reports.
7.6 prestressing anchorages and connectors
of the certification and inspection records.
7.7 tensioning equipment calibration
record.
7.8 tensioning records.
7.9 pressure test for strength of
prestressed duct Grouting block report and cement factory certificate.
7.10 strength of concrete test block, and
block test report.
7.11 the design requirements of other
relevant information.
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