Study On Fatigue Performance And Maintenance & Planning Methods Of Decks Of RC Ribbed-Girder Bridges In Service

As a classical bridge type,RC ribbed-girder bridges are widely applied in China.In China,highway bridges bear increasing traffic loads due to more vehicles on roads and have deteriorating performance gradually.With repeated interaction with vehicle loads,fatigue issues of these bridges must be solved.For these bridges,concrete decks are the part which easily suffers from fatigue load during operation.Many old bridges in service have worsening or even grooved decks due to the inaccurate prediction of the future trafic during construction.To ensure the operation safety of old bridges and provide reference to evaluation,maintenance,reinforcement,and design,it is practically significant to study the fatigue performance evaluation and reinforcement methods of decks.Since 2017,a comprehensive test study and theoretical analysis has been conducted to the fatigue performance evaluation and reinforcement methods of the deck of RC ribbed-girder bridges,including 3 girders for benchmark test,4 for fatigue test,3 for benchmark reinforcement,3 for fatigue reinforcement test,and 6 anchor specimens for test,as well as the analysis on fatigue failure mode and evaluation system,fatigue performance,fatigue reinforcement performance,additional anchoring,fatigue maintenance and planning.The work details are shown below:(1)Based on 15 bridges,this paper investigates fatigue failure of slabs on in-service reinforced concrete bridges with ribbed beams over the past 10 years in China;selects two typical bridges therein for testing real conditions of their slabs;and compares domestic and foreign standards for fatigue failure of slabs on existing reinforced concrete bridges with ribbed beams.According to the investigation results,86.7%fatigue holes on these bridge slabs have an area less than 3m2 and mainly result from punching shear failure.Mostly,this fatigue failure has occurred within 30 years,which is over 10-year shorter than normal fatigue period.After construction for 10 to 20 years,about 46.7%bridges have occurred fatigue failure,and life of such fatigue failure is seriously lower than the designed value.One of the key factors that influence fatigue failure on bridge slab is reciprocation of loaded vehicles.However,resurfacing the bridge slab cannot delay such fatigue failure.Moreover,there is not a fatigue evaluation system for slabs on reinforced concrete bridges with ribbed beams in China.(2)This paper selects a reinforced concrete bridge with 16m span and T-shape ribbed beams and designs a test bridge with span 4m with scale similar to 1:4;measures ultimate bearing capacity of slabs on two standard test bridges with length-width ratio 6.5 and 1.88 through static test;and takes fatigue load value 0.515 for fatigue loading test under equivalent amplitude at fixed point on three test bridges with length-width ratio 6.5,3.76 and 1.88.According to test results,the surface slab occurs radial fracture and punching shear failure under the effect of fatigue load.The specific value of fatigue life of slabs on test bridges with length-width ratio 6.5,3.76 and 1.88 is 1:1.228:1.396.Under same fatigue load,the fatigue performance of two-way slab is better than the one-way slab.(3)Based on the fatigue test,the finite element analysis model for fatigue damage is created for test bridges with ABAQUS to respectively analyze influences of length-width ratio,fatigue load,and slab thickness on fatigue performance of the bridge slab and discuss S-N curve of slab on reinforced concrete bridge with ribbed beams.Based on simulation and analysis,the length-width ratio of the bridge slab declines from 6.5 to 3.76 and 1.6 and fatigue life respectively increases 15%and 33%.The fatigue life of two-way slab is about 20%longer than the one-way slab,while the fatigue load declines from 0.383 to 0.271 and fatigue life increases 54%.When the slab thickness increases 12.5%,its fatigue life increases about 15%.Under same fatigue load and frequency of fatigue damage,residual loading capacity of the bridge slab with small length-width ratio is higher than the slab with high length-width ratio.Besides,impacts of the slab thickness on fatigue performance of the slab is larger than length-width ratio,but lower than fatigue load.(4)The bar-type steel plate,carbon fiber cloth and grid are used for fatigue reinforcement for the bridge slab.Besides,this paper selects the test bridge with length-width ratio 2.8 as slab reinforcement object to successively conduct static damage test,and fatigue loading test under equivalent amplitude with fatigue load 0.515 at fixed point;and discusses S-N curve of the bridge slab under fatigue reinforcement.According to the test results,when load cycle frequency reaches over 90%of the fatigue life,reinforced slab occurs major fatigue fracture at the loading point.For slab without reinforcement and slab reinforced with carbon fiber cloth,carbon fiber grid,and bar-type steel plate,the specific value of their fatigue life is 1:1.754:1.789:1.533.After slab reinforcement,the fatigue life increases 53.3%?78.9%and degradation evolves slowly.During fatigue development,slab degradation declines over 50%with above reinforcement materials.Under same fatigue load,the carbon fiber cloth and grid have better fatigue reinforcement effect than the bar-type steel plate.(5)Through loading test for six test slabs,this paper analyzes appropriate anchoring method for one-way slab reinforced with carbon fiber cloth;and studies interlayer adhesive performance between carbon fiber cloth and slab structure based on characteristics of surface reinforcement on the bridge slab.According to experimental results,the non-enclosed carbon fiber strips are mainly used for anchoring,while enclosed carbon fiber strips are mainly used for achieving anchoring effect,which is better than interval anchoring with non-enclosed carbon fiber strips.The steel plate strips are mainly used for bolt anchoring,and debonding failure on bridge slab occurs on interval anchoring.The carbon fiber strip has a stronger capacity of resisting debonding damage of carbon fiber cloth than the steel plate strip.When the one-way slab on reinforced concrete bridge with ribbed beams is reinforced,it is appropriate to use non-enclosed carbon fiber strips for anchoring.The shear strength and bonding strength between structural layers and the bridge slab with carbon fiber meet requirements.(6)Based on the compromise programming and fault tree programming,this paper creates the fatigue maintenance and programming model for slabs on in-service reinforced concrete bridges with ribbed beams in accordance with maintenance planning concept of mechanical equipment;and analyzes the relationship between fatigue life of bridge slab and different failure probability with Weibull distribution theory.If the fatigue load is taken to 0.515,the failure probability of this model is less than 0.01 when time node for fatigue maintenance is 0.4 times of the fatigue life,and the failure probability of this model changes from 0.00011 to 0.000013 when time node for fatigue maintenance is 0.2 times of the fatigue life.