Current Practices and Guidelines for the Reuse of Bridge Foundations (2017) / Chapter Skim
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From page 43... ...
43 chapter four Case examples The survey results presented in chapter three were used to select five agencies for further case examination. The agencies were primarily identified based on responses that revealed that the agency had unique policies related to foundation reuse, frequent experience with foundation reuse, or experience on noteworthy foundation reuse projects.
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44 predict capacity by means of static analysis methods and performing a static load test to 2.5 times the proposed design load. MaineDOT's Bridge Design Guide also includes provisions regarding reuse of granite and stone abutments.
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45 tion as scour-critical. For bridges identified as scour-critical, investigation of scour countermeasures is included in design of the rehabilitation project.
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46 footings were recommended for reuse pending further evaluation in final design, including analysis of lateral load. The feasibility of reusing the driven piles was evaluated by comparing the predicted vertical pile loads for the rehabilitated bridge with the pile design loads shown on the final plans for the original bridge construction.
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47 Test pits at four of the piers were excavated to depths below the pile caps to inspect the piles for evidence of corrosion. Photographs of the test pit investigation are shown in Figure 31.
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48 as a three-span steel girder bridge with two mass concrete stub abutments on treated timber piles and two solid wall piers on untreated timber piles. A 2014 MaineDOT inspection report revealed several concerns with the superstructure: fracture-critical pin connections in serious condition, structural steel in overall poor condition (nBI condition rating 4)
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49 Subsurface conditions at the Haynesville site generally consist of alluvial sand with silt and gravel over glacial deposits of sand, silt, and gravel. Bedrock is encountered beneath the glacial deposits, with the top of the bedrock generally 25 to 35 feet beneath the riverbed.
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50 Under Static Axial Compressive Load (2013)
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51 the jack pressure was "significantly lower" than the load indicated by the load cell, which was used to develop Figure 34. Also, as described previously, wedges had to be used to remove the 19-inch segment from the south abutment test piles.
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52 projects. The agency was confident that its foundation design practices had historically been inherently conservative.
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53 problems. The outline for the updated policy is similar to the original policy, maintaining the use of abbreviated and detailed methods.
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54 2. Dynamic formula bias: IDOT used the Engineering News Record (ENR)
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55 lic models are generally not available when such models are developed. The agency reported that resulting scour predictions are typically severe, indicating scour depths as great as 40 feet below the mudline.
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56 geotechnical, and hydraulic procedures related to reuse. Information about the agency's experience with reuse, its evaluation criteria for reusing foundations, and examples from preliminary structures reports are presented in the following sections.
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57 being considered for reuse, which can be considered using the HS-25 live loading from previous AASHTO standards. More lenient exceptions are also granted for reusing historical substructures.
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58 using conventional construction methods or using ABC methods and (2) whether to replace the substructure, reuse it as-is, or reuse it with rehabilitations.
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59 example psr: Hunt road over i-495 The bridge carrying Hunt Road over I-495 outside of Lowell, Massachusetts, was constructed in 1969. A PSR was prepared recently (McFarland & Johnson, Inc.
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60 massDot: lessons learned MassDOT reported more instances of foundation reuse than most other U.S. agencies.
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61 The substructures were constructed using normal weight concrete and were founded on rock with steel H-piles, spread footings, or timber piles. After 40 to 50 years of service, most of the superstructures had deteriorated considerably, exposing the concrete reinforcement and requiring superstructure replacement.
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62 truss supported on massive pneumatic caissons keyed into bedrock. In 2012, MoDOT intended to replace the bridge but reuse the pneumatic caissons.
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63 moDot: lessons learned For MoDOT, foundation reuse is an important cost-saving tool that has seen increased implementation in the last ten years. The agency has several hundred bridges with scour action plans; those bridges are more likely to involve complete bridge replacement rather than reusing the foundations.
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64 The wildlife certification requirements have motivated foundation reuse for many small, rural bridges over streams. For such bridges, the abutments are often left in place when replacing the superstructure to avoid the need for construction activity in the stream.
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65 design plans to the value required for the new structure to determine if additional foundation elements or other modifications would be required. Such modifications may deem reuse to be impractical.
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66 To address foundation concerns, MTO and its consultant considered replacing the entire bridge, enlarging the problematic footings and installing additional driven piles or drilled shafts, and underpinning the problematic footings with micropiles. Of those, underpinning with micropiles was the only option that satisfied project schedule constraints, including mobility concerns, as well as environmental restrictions that permit in-water operations only during an approximately 50-day window each summer.
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67 a 2-inch-diameter center bar. The casings were installed through the existing foundations and 2 feet into bedrock, and the micropile bond zone extended 8 feet below the casing.
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68 that one lesson learned from the Rosseau River Bridge replacement was that underwater inspection of the footings should have been performed as part of the condition assessment supporting the 1982 superstructure replacement as well as for the 2015 planned rehabilitation. mto: lessons learned The experience of MTO with foundation reuse is similar to that of U.S.
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69 of recommending reuse, and MaineDOT, MassDOT, and MTO provided example projects that were designed by consultants. The resulting picture of consulting practice for foundation reuse projects is unclear, but it appears likely that the uncertain standard of care noted in the literature review (Brown 2014)
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