Bridge Deck Construction

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METHODS AND MATERIALS

Bridge Prototype

The prototype of the bridge was built to full scale with a few modifications. Shows a comparison between the prototype bridge deck and the proposed actual bridge deck.  The prototype is only three girders wide with an overhang on each side as opposed to six girders wide with an overhang on each side.  The overall width of the bridge deck is 17 ft 4 in. and the length is 24 ft.  The deck also has four 1 ft by 2 ft block outs, two on either side, to accommodate the columns for a load frame.

Placing the Concrete

The concrete was placed using a ¾ cubic yard bucket.  The concrete was vibrated as it was placed to ensure that all voids were filled and that no honeycombing took place. A screed rail was placed along the width of the deck at approximately 11 ft from the North end so that the deck could be poured using two separate pours and concrete batches.  Two separate pours had to be made with two separate concrete batches because of equipment limitations: the limited screed length and the concrete truck capacity.  The total amount of concrete used was approximately 11 cubic yards, but the maximum truck capacity is about 7 cubic yards, so two separate trucks with batches of 6 and 5 cubic yards were used. After both pours were complete, the screed rail was removed and the void was filled in with concrete.  The surface was then finished and 4 in. diameter cylinders were made for each batch of concrete to measure the strength gain over time. The deck was covered with plastic sheeting and watered for seven days to obtain a seven day moist cure.  The cylinders were match cured to the deck.  The formwork was stripped after 12 days.

Materials

Concrete

The type of concrete used for the deck was a VDOT A4 mix, which is a standard mix for bridge decks.  The A4 mix is a 4000 psi mix that has ¾ in. aggregate, a watercement ratio of 0.45, typical slump of 2 in. to 4 in., and air content of 6.5% ± 1.5%.  As aforementioned, 4 in. diameter compressive test cylinders were made for both of the batches used in the bridge deck.  Batch 1 was placed in the East half of the slab and batch 2 was placed in the West half of the slab, both batches exceeded their 4000 psi minimum strength and batch 2 had a higher strength than batch 1.

Instrumentation and Test Setup

Overhang Tests #1 & #2

Overhang Tests #1 and #2 were designed to simulate a typical AASHTO design truck tire on the edge of the overhang, which would create a negative moment in the deck over the exterior girder.  This load is harsher than reality, because the bridge will have a barrier rail on the overhang that will prevent a wheel load from being applied to the overhang.  The instrumentation and test setup for overhang tests #1 (South side) and #2 (North side) were almost identical.  The only difference between the two were slight differences in strain gauge locations.  These differences were no more than ½ in. and were due to human error in placing the bars.

Instrumentation 

Each of the two overhang tests had eight No. 5 transverse GFRP bars strain gauged and four No. 6 transverse steel bars strain gauged.  Both the GFRP and steel strain gauges were positioned along the outer edge of the exterior girder’s flange.  This distance measured 21 in. from the North and South sides for tests #1 and #2, respectively.  For Overhang test #1, North side, the gauges were positioned as shown in Figure 3.14, and all the gauges were 2 3/8 in. from the top of the slab. For Overhang test #2, South side, the gauges gauges were positioned as shown in Figure 3.14, and all the gauges were 2 ½ in. from the top of the slab.  The steel gauges were positioned as shown in Figure 3.15  the slab, and were 2 ¼ in. from the bottom of the slab for both tests.  All of the strain gauges for all of the tests were oriented along the length of the particular bar that they were affixed to.

Interior Girder Test

The interior girder test was performed to simulate a typical AASHTO design truck traveling over the center of an interior girder with its axle perfectly straddling the girder.  This creates a maximum negative moment over the interior girder.

Instrumentation

This test utilized ten steel strain gauges and twelve GFRP gauges, all of which were located on transverse bars.  Six GFRP bars were gauged, with two gauges on each bar.  The gauges were 10 in. apart and the bars were positioned so that the gauges were on either edge of the interior girders top flange.  The distance to the gauges measured 99 in. from the South side to the first gauge and an additional 10 in. to the second gauge, a total of 109 in.  The gauges were also set up to straddle the middle support with three equally spaced rows on either side.  The rows of two gauges were positioned as shown in Figure 3.14.  All of the GFRP gauges were approximately 2 3/8 in. from the top of the slab. Two of the steel strain gauges were positioned similarly to the GFRP gauges in that they were placed on either edge of the interior girder’s top flange.  They were located 130 in. from the East end.  The remaining eight were on four different bars, two per bar.  They measured 67 ½ in. and 139 in. from the North side of the slab, respectively.  This placed the gauges under the load points to measure stresses at the location of maximum positive moment.  The pairs were positioned as shown in Figure 3.15.  All of the gauges were 1 ¼ in. from the bottom of the slab. The wire pots used to measure deflections were in the same locations on both sides of the interior girder.  They were anchored to the bottom of the slab at 3 ft. 3 in. from the centerline of the interior girder to either side.  The first pot on either side was located 9 ½ ft from the East end of the slab, and the other two on either side were positioned 18 in. on center from the first .

Test Setup

The two columns for the load frame were placed in the notched out sections of the slab 11 ft from the East end.  The columns were bolted to the reaction floor beams and the crossbeams were bolted to the columns.  A 400 kip capacity hydraulic ram and a 500 kip capacity load cell were hung from the crossbeams directly over the interior girder.  The load was applied to the slab through two 8 in. by 20 in. neoprene pads with steel plates placed on top of them.  The centers of the pads were placed 3 ft to either side of the centerline of the interior girder and 11 ft from the East end.  A spreader beam was placed on top of both load plates running along the width of the slab.  The ram applied load to the center of the spreader beam, which applied two equal loads to the patches

Cantilever Test

The cantilever test was performed to simulate negative moments over interior supports in continuous span structures.  Even though the actual design comprises simple spans, this test was performed to examine the behavior of GFRP reinforced decks in continuous spans.

Instrumentation

This test utilized eleven GFRP strain gauges, eight steel strain gauges on reinforcing bars, and six steel strain gauges on the girders.  Of the eleven GFRP strain gauges, three were positioned on longitudinal bars over the centers of each girder, six were positioned on longitudinal bars on either edge of the top flange of each girder, and the other two were positioned on longitudinal bars halfway between the three girders. They were positioned as shown. They all measured 59 ½ in. from the West edge of the slab and 2 7/8 in. from the top of the slab. Of the eight steel reinforcing bar strain gauges, six were positioned on longitudinal bars on either edge of the top flange of each girder, and the other two were positioned on longitudinal bars halfway between the three girders.  They were positioned as shown in Figure 3.15. They all measured 59 ½ in. from the West edge of the slab and 1 7/8 in. from the bottom of the slab.  All of the six steel strain gauges on the webs of the three girders measured approximately 58 in. from the West end of the girders.  On each girder, one gauge was located approximately 3 7/16 in. from the bottom of the girder, and one was located approximately 3 7/16 in. from the top of the girder. The three wire pots used on this test were attached to the bottoms of each girder with a magnet.  The pots were positioned right on the West end of each of the girders (Figure 3.16).

Test Setup

The two columns for the load frame were placed in the notched out sections of the slab at the West end.  The columns were bolted to the reaction floor beams and the crossbeams were bolted to the columns.  Three 400 kip capacity hydraulic load rams were used for this test.  One was hung over each of the girders.  The two rams over the exterior girders were hung with 200 kip capacity load cells and the ram over the interior girder was hung with a 500 kip capacity load cell.  Load was applied to the slab through 5 in. by 5 in. neoprene pads with steel plates on top of them.  The pads were located over the top of each girder and they were all 1 ft from the West end (Figure 3.19).

Test Procedures

All of the instrumentation devices; the strain gauges, wire pots, and load cells, were connected to the System 6000 data acquisition system.  The Strain Smart software program was used to record the data.  All the channels of the data acquisition system were zeroed and an online display of all the channels and their readings was created so the data could be monitored during testing.

Overhang Tests #1 & #2

A preload of 5 kips was applied to the overhangs to allow the structure to settle and the overhangs were then unloaded.  Load was applied to the overhangs in 2 kip increments and data was recorded at each increment.  This was continued until it was determined that the section was cracked, 30 kips for test #1 and 32 kips for test #2.  The overhangs were then unloaded and reloaded up to a service wheel load times an impact factor, 21 kips.  This was done three times to represent the cycling of traffic the bridge would see and data was recorded at each load stage. The overhangs were loaded again from the previous load in 2 kip increments until a total load of approximately 40 kips was on the overhang.  At this point, the load increments were increased to 4 kips up to failure, and data was still recorded at each increment. Throughout the entire process, the overhang was continuously checked for cracks and the crack widths were measured using crack cards.  The Whittemore gauge readings were also taken at various loads throughout the testing. During test #1, after a load of 65 kips had been reached, it was discovered that the ram was putting a torque on the crossbeam.  This was in turn was putting a torque on the entire frame and causing the columns to bend.  The test was stopped and the columns were braced.  The test was started again and loaded in 10 kip increments up to the previous load of 65 kips.  The overhang was then loaded up to failure in 5 kip increments.

Interior Girder Test

A preload of 10 kips was applied to the spreader beam, 5 kips per patch load, to allow the structure to settle and then the deck was unloaded.  The load was applied to the spreader beam in 10 kip increments up to a load of 160 kips and data was recorded at each increment.  The increments were then increased to 20 kips up to failure. The deck was continuously checked for cracks throughout the test.  Once cracking occurred, some of the cracks were labeled and their widths were measured at various loads using a crack microscope.

Cantilever Test

The two exterior hydraulic load rams for this test were connected in series and the interior ram was connected separately.  The loads were kept about equal on each ram by using the online display of the loads as measure by the load cells. A preload of 10 kips was applied to each ram to allow the structure to settle and then the bridge was unloaded.  Load was applied to the cantilever through each ram in 10 kip increments and data was recorded at each increment.  This was done until it was determined that the section was significantly cracked, 110 kips on each ram.  The cantilever was then unloaded to 10 kips and loaded up to a service load, about 80 kips. This was done five times to represent the cycling of traffic the bridge would see and data was recorded at each load stage.  The load was taken back up to 110 kips and continued in 10 kip increments until a load of 140 kips was reached.  The section was not failed due to inadequate capacity of the load cells and load frames. The deck was continuously checked for cracks throughout the test.  Once cracking occurred, some of the cracks were labeled and their widths were measured at almost all load increments, including the service cycling, using a crack microscope.

1: INTRODUCTION
1.1: Background
1.2: Objectives
1.3: Thesis Organization
2: LITERATURE REVIEW
2.1: Material Properties
2.2: Mechanical Properties
2.3: Experimental Results and Designs
2.4: Conclusions and Recommendations
3: METHODS AND MATERIALS
3.1: Bridge Prototype
3.2: Bridge Deck Construction
3.3: Materials
3.4: Instrumentation and Test Setup
3.5: Test Procedures
4: RESULTS AND DISCUSSION
4.1: Overhang Tests #1 & #2
4.2: Interior Girder Test
4.3: Cantilever Test
5. CONCLUSIONS AND RECOMMENDATIONS
5.1: Introduction
5.2: General Conclusions and Recommendations
5.3: Validity of Actual Design
5.4: Constructability
5.5: Recommendation for Further Research
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LABORATORY TESTS OF A BRIDGE DECK PROTOTYPE WITH GLASS FIBER REINFORCED POLYMER BARS AS THE TOP MAT OF REINFORCEMENT

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