How does the comb plate expansion device perform in low-temperature environments
The performance of the comb plate expansion device in low temperature environments (usually referring to temperatures ≤ -10 ℃, and can be as low as -30 ℃ in severe cold areas) is influenced by three core factors: material characteristics, structural design, and installation processes. The overall performance shows the characteristic of "retaining rigid advantages but highlighting flexible shortcom
The performance of the comb plate expansion device in low temperature environments (usually referring to temperatures ≤ -10 ℃, and can be as low as -30 ℃ in severe cold areas) is influenced by three core factors: material characteristics, structural design, and installation processes. The overall performance shows the characteristic of "retaining rigid advantages but highlighting flexible shortcomings", which can be analyzed from two aspects: failure risk and optimization measures:
1、 Typical Failure Risks in Low Temperature Environments (Key Attention Required)
If no special design or maintenance is carried out for low-temperature environments, the comb plate expansion device is prone to the following failure problems, which directly affect the service life of bridges and driving safety:
Deformation or fracture of comb plate
If ordinary carbon steel (such as Q235) is used for the comb plate in extremely cold regions, the toughness at low temperatures is insufficient. When heavy vehicles crush it, the stress concentrated parts of the comb teeth (such as the tooth roots) are prone to "brittle cracks", which may break after long-term use, resulting in "steps" at the expansion joint and causing vehicle bumps and even tire blowouts.
Loose or detached fixing bolts
The difference in thermal expansion and contraction coefficients between metal bolts and concrete embedded sleeves at low temperatures (the linear expansion coefficient of steel is 12 × 10 ??/℃, while that of concrete is 7 × 10 ??/℃) can lead to an increase in thread clearance, and coupled with the vibration effect of freeze-thaw cycles, the bolts are prone to gradually loosen; If bolts are not treated with anti-corrosion measures (such as hot-dip galvanizing), low-temperature and humid environments will accelerate corrosion, leading to bolt fracture and displacement of comb plates.
Freeze thaw damage at the end of the beam
After the seal fails, rainwater seeps into the concrete at the end of the beam below the comb plate. Freezing and expansion at low temperatures can cause the concrete to "loosen and peel off", exposing the internal steel bars; The volume expansion of corroded steel bars further exacerbates concrete cracking, forming a "vicious cycle" that can seriously affect the structural safety of bridge beams.
2、 Performance optimization measures in low-temperature environments (improving applicability)
To improve the performance of the comb plate expansion device in low-temperature environments, targeted optimization is needed from three aspects: material selection, structural design, installation and maintenance
Material selection: Prioritize the use of low-temperature adaptive materials
Comb plate: Made of low-temperature tough steel (such as Q355ND, Q460ND), ensuring an impact energy of ≥ 34J at -40 ℃ to avoid brittle fracture; The surface can be treated with "hot-dip galvanizing+passivation" (zinc layer thickness ≥ 85 μ m) to enhance low-temperature corrosion resistance.
Sealing components: Use low-temperature elastic rubber sealing strips (such as EPDM rubber, glass transition temperature ≤ -50 ℃) or low-temperature curing sealants (such as modified silicone adhesive, suitable for temperatures -30 ℃~80 ℃) to avoid low-temperature hardening and cracking.
Sliding support: Low temperature polytetrafluoroethylene sliding plate (reinforced with glass fiber, low-temperature friction coefficient ≤ 0.04) is used, or "low-temperature grease" (applicable temperature -40 ℃~120 ℃) is applied between the sliding plate and the stainless steel plate to reduce sliding resistance.
Structural design: Strengthen resistance to freeze-thaw and displacement compatibility
Add "drainage redundancy": Design double-layer drainage channels (main channel+spare channel) at the bottom of the comb plate, and increase the diameter of the drainage holes (≥ 50mm) to accelerate rainwater drainage and reduce the chance of water accumulation freezing; At the same time, "anti-seepage and water blocking strips" are installed at the end of the beam to prevent rainwater from penetrating into the concrete.
Reserve "low temperature gap": During installation, an additional 5-10mm low temperature shrinkage gap should be reserved according to the local lower temperature (for example, 15mm should be reserved for installation at room temperature, and 10mm should still be reserved after shrinkage at low temperature to avoid comb teeth jamming); For curved bridges with significant lateral displacement, "arc-shaped comb plates" or "lateral guide grooves" are used to enhance displacement flexibility.
Strengthen the "connection strength": High strength low-temperature bolts (such as grade 8.8 or above, with zinc infiltration anti-corrosion treatment) should be selected for fixing bolts, and a "double nut anti loosening" design should be adopted; The welding between the comb plate and the embedded steel plate adopts "low-temperature welding rod" (such as J507NiCrMoV), and after welding, "stress relief heat treatment" is carried out to avoid low-temperature cracking of the welded joint.
Installation and maintenance: Suitable for low-temperature construction and regular inspections
Low temperature installation requirements: When the construction temperature is below -5 ℃, the concrete foundation needs to be "preheated" (using electric blankets or hot air guns to ensure that the foundation temperature is ≥ 5 ℃) to avoid hollowing of the joint surface between the concrete and the comb plate due to low temperature; Before applying sealant, it is necessary to remove ice and snow from the gaps between the teeth to ensure a tight bond between the adhesive layer and the metal surface.
Regular maintenance focus: Before the arrival of winter, clean the snow, ice, and debris in the gaps between the comb teeth to avoid damage to the comb teeth due to frost heave force; After the spring snow melts, check whether the sealing components are intact. If the sealing strip cracks or the sealant falls off, replace and repair it in a timely manner; Check the fixed bolts every six months, tighten loose bolts, and replace corroded bolts in a timely manner.
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