6. RESULTS

6.1 Tests

A significant amount of data involving 560 data sets has been obtained from both tests. Here each data set consists of all measured results for a particular quantity (crack displacement, intrados macro strain or anchor strain) on one instrumented line and for one span, see Figure 4.3. To avoid excessive amounts of data-processing the results described in this report focus on the six most extreme vehicle load cases as described in section 4.3, and for strain measurement comparisons, consider only those results taken for the South span. The basis for selecting these data sets is further explained below.

1. Load cases LC7, LC8 and LC9 over the South span and LC10, LC11 and LC12 over the north span have been considered for crack width displacement comparisons. Apart from generating the largest displacements and strains these load cases are also influenced the least in terms of transverse load distribution boundary effects; the applied load spreading laterally to unloaded parts of the bridge.
    
2. Results corresponding to load cases LC8 and LC9 have been presented for discussion of trends based on Intrados macro strain measurements. More gauges worked successfully for the South span for both tests than the North span. These same load cases have also been used to assess the behaviour of the anchors in the second test.

The results of these representative load cases, six for crack measurement and two for strain results, applied to both the unstrengthened and strengthened bridge are set out here and discussed in section 6.

6.1.1 Vertical Displacement

Vertical displacements were recorded in the first test but, as anticipated, they were negligibly small under the applied serviceability loads and meaningful interpretation was difficult. Other monitored parameters produced much more useful data and thus detailed consideration of the vertical displacements is not presented here.

6.1.2 Crack Monitoring

Displacements across the four transverse cracks which were monitored during both tests are summarised in Figure 6.1. Positive values indicate cracks opening. Plan inserts showing the vehicle arrangement used for each load case are included, and viewed in plan the values for crack displacements appear adjacent to the approximate crack locations.

Exact crack positions are shown in Figure 2.2. No results were obtained from the North East gauge in the South span.

Crack Displacements [mm x 0.001] – RED Unstrengthened, BLUE Strengthened
South Span – Double Vehicle Load Cases
2	1		2	2	0		3	2	0		2
-3	-2		-11	-2	-2		-27	-2	-2		-14
LC 9				LC 8				LC 7
-6	-6	6	-12	-7	-6	-10	-24	-6	-5	-5	0
2	2	1	3	2	2	3	1	2	2	3	2
North Span – Double Vehicle Load Cases
-3	3		6	9	4		2	6	2		2
8	-10	6		-46	-12	2	9	-28	-10	2	9
LC 10				LC 11				LC 12
-19	-7	2	8	-46	-12	2	9	-28	-10	2	9
2	2	1	2	4	2	1	2	3	2	1	1

Figure 6.1 – Displacements Across Cracks During Load Tests

6.1.3 Intrados Strains

The intrados macro strain measurements, taken using 0.5m gauge lengths to record average strains resulting from both brick unit/mortar and crack behaviour, has provided data sets for both tests in most locations for all 28 load cases. Some gauges were lost due to water damage during the installation of strengthening; 28% on the North span, 5% on the South span.

Representative results are illustrated in Figure 6.2a and 6.2b for load cases LC8 and LC9 respectively. The results are presented for the eighteen gauges around the intrados of the south span on the east instrumented line; approximately along anchor line 8, see Figure 4.3. Macro strains are plotted against gauge number for the unstrengthened (red curve) and strengthened (blue curve) tests. The position of gauges 55 and 72 mark the north and south springings of the arch respectively and gauges 63 and 64 are at mid-span. Positive values indicate tensile strains. Vertical dotted lines mark the location of the cracks and indicate the gauges that would therefore span cracks.

Load case LC8 – A pair of 11.4 tonne axles at mid-span of the south span

Figure 6.2a Representative Intrados Macro Strains

Load case LC9 - A Pair of 11.5 tonne axles at pier quarter-span of the south span

Figure 6.2b Representative Intrados Macro Strains

6.1.4 Anchor Strains

Anchor strains along the length of the eight instrumented anchors were recorded for the strengthened tests and all 28 load cases. The 112 gauges were arranged in pairs and a total of 9% failed to operate correctly or were damaged during installation, leading to no significant loss in recordings. All measured results lay between a minimum value of -51 µå and a maximum value of 30 µå.

Figure 6.3 shows the measured strains for the south span, east side corresponding to load cases LC8 and LC9. Micro strains are plotted against their relative position along the two anchors, see Figure 4.1; numbers 77 to 111 relate to the anchor in the north half of the span, numbers 115 to 149 to the anchor in the south half.

Figure 6.3 Representative Anchor Strains – East side of South Span

6.2 Predicted

Using the numerical model described in section 5, intrados macro strains and anchor strains have been calculated at similar locations to the instrumentation used in the tests. Average strains have been calculated over a 0.5m length for direct comparison with measured values and include the effects of elastic strain and mortar gaps opening. Although the cracks have been included as discontinuities in the model they have been modelled as initially closed for simplicity. Thus where application of live load has caused closure of previously open cracks these movements have not been predicted.

Figure 6.4 shows the results of a typical test simulation and in this case illustrates principal compressive stresses in the barrel and file.

Show principal compressive stresses; blue, green, yellow shoe increasing levels of compression

Figure 6.4 Typical Predicted Results – South Span, Load Case LC9