Click for next page ( 10


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 9
9 Integral Connections typically provide stay-in-place form- classification, and evaluation of each individual connection work in which two adjacent members can be monolithically are presented in a standardized form and are summarized for connected. An example of an integral connection is a steel each connection type in this report. The details for each con- diaphragm/cap beam of a composite bridge that is filled with nection are provided in the appendices. The three measures site-cast concrete to connect a concrete column. The inte- then indicate three different, but necessary, characteristics of gral connection requires the largest in-situ concrete pour of the connection types: all connections previously described. Emerging Technologies, Deformation Elements, and Mis- Technology Readiness Level--the level of development. cellaneous Types are in a class of connections that includes Performance Potential--the potential merits and disadvan- the various improvements proposed to either existing con- tages in terms of performance. nection types, such as the hybrid type, or entirely new types Time Savings Potential--the potential for accelerating the of connections, that use new materials or advanced materi- construction schedule. als in new ways. Examples are the use of elastomeric bearings incorporated with columns and the use of shape-memory Furthermore, an evaluation procedure was developed for alloys (SMAs). The class also includes connections that the assessment of the performance of entire bridge systems might be used to relieve internal forces and, thus, primarily composed of suitable combinations of the individual connec- accommodate deformations. These types of connections tion types analyzed. The following paragraphs explain the are called deformation elements. They are included in the development of the various measures. same type class as emerging technologies, because those connections are often used similarly to accommodate Technology Readiness deformations. Mechanical Connections are bolted, welded, or provide All the connections were assessed according to their readi- mechanical devices to connect two adjacent members such ness for implementation in accelerated bridge construction in as a bridge bearing. seismic areas. In particular, if connections used newly devel- oped technologies, the assessment provided insight into the In the connections that have been evaluated, proprietary requirements for complete deployment in the field or, failing hardware is commonly found. In some cases, there are multi- that, described the activities required to move the technology ple vendors of similar products so that sole source procure- to the next level. ment of the hardware is not an issue. However, for some types The U.S. Department of Energy (DOE) provides a process of connection hardware, this is not the case. The user should for this type of evaluation and calls it Technology Readiness be aware of this when considering a connection for potential Assessment. The process was originally developed by the use on a project. In this report, no effort has been made to iden- National Aeronautics and Space Administration (NASA) and tify the connection hardware by manufacturer, and in fact, the has since found its application in the U.S. Departments of opposite is true. The report sought to avoid identification of Defense and Energy, as well as in related industries. The process specific manufacturers. In the categories above, the ones that is defined by a scale of nine steps, referred to as technology typically have the potential for sole-source proprietary hard- readiness levels (TRL), that describe the readiness state of a new ware that could affect the detailing are bar couplers, emerging or newly applied technology, from TRL 1 (an observation) to technologies, and mechanical connections. TRL 9 (a fully implemented and functional technology). Typ- ically, the process focuses on the assessment of a particular technology in a particular environment. A guideline can be Evaluation Methodology found in the U.S. Department of Energy's Technology Readi- Connection details were assembled from the questionnaire ness Assessment Guide (2009). The TRL levels defined by the responses and from other sources in the literature review DOE are given in Table 2. phase. Each connection detail was evaluated to appraise its fit- An attempt was made to apply these nine levels of readiness ness for use and its potential performance during construc- directly to SABC. However, the DOE definitions were found to tion, service, and a seismic event. A set of evaluation criteria be a poor fit for the important characteristics of ABC, despite was developed that included the following: practical experi- their apparent generality. Thus, a new scale, similar in intent ence with an individual connection, measures for the evalua- but different in detail, was developed. The new scale is shown tion of the technology, readiness of the connections for seismic in Table 3. application, the type of seismic performance, and the practi- A TRL value of 1 is applicable to all connection types in the cal characteristics of the connections, such as constructability, database because their presence there indicates that a concept durability, inspectability, and reparability. The characteristics, has at least been formulated.

OCR for page 9
10 Table 2. Original definition of technology readiness level (DOE). Level Definition per DOE 1 Basic principles observed and reported 2 Technology concept and/or application formulated 3 Analytical and experimental critical function and/or characteristic proof of concept 4 Component and/or system validation in laboratory environment 5 Laboratory scale, similar system validation in relevant environment 6 Engineering/pilot-scale, similar (prototypical) system validation in a relevant environment 7 Full-scale, similar (prototypical) system demonstrated in a relevant environment 8 Actual system completed and qualified through test and demonstration 9 Actual system operated over the full range of expected conditions In TRL 2, either analysis or testing is deemed acceptable for single test and significant analysis, including studies of the verification of static strength. Analysis is deemed acceptable for influence of the important parameters in the design. this purpose because member design for static response, such TRL 8 provides verification of constructability when seismic as bending of beams, is conducted without question using details are used. It is also deemed to satisfy the requirements of analysis alone. TRL 3. TRL 3 provides a basic verification of constructability. If the TRL 9 provides verification that the connection satisfies the connection concept is used in a seismic region, the bar conges- twin requirements of constructability and seismic perform- tion may be more severe and the connection may be less read- ance. Few, if any, connections can be expected to achieve ily constructible than its non-seismic counterpart. However, a TRL 9 because ABC connections have been used in bridges TRL of 3 indicates that there are no fundamental impediments only in recent years and have rarely been built in high-seismic to construction. regions. A full-scale dynamic shaking table test does not qual- TRL 4 indicates that the connection type has been evaluated ify as a TRL 9. analytically for seismic loading. The analysis should include the The technology readiness assessment procedure was applied effects of cyclic loading and inelasticity, including ductility to each identified ABC connection to evaluate its readiness for demand and capacity. It is also deemed to satisfy the require- application in seismic regions. As part of the summary, the ments of TRL 2. individual connection types were also evaluated for the extent TRL 5 demonstrates by test the viability of the critical the connections met the TRL in terms of percentage completed components. For example, in a connection that depends on for each level. The evaluation table can be seen in Table 4. The mechanical couplers to transfer tension between bars, TRL 5 evaluation allows identifying gaps in the current knowledge of might apply to an individual coupler. The testing must, of a connection type. Ideally, a TRL is met 100% before the next course, be successful for TRL 5 to apply. level is started. However, in reality, some levels are skipped or TRL 6 refers to testing of a complete connection, such as a deemed satisfactory after partial completion. A skipped or par- column-to-cap beam moment connection, rather than to a tially completed level does not necessarily mean that a knowl- component, such as a bar coupler. edge gap exists, as later development steps might fill such gaps. TRL 7 represents an important step towards field imple- But gaps in the TRL indicate risks that problems might show mentation. The existence of guidelines implies more than a up later in the development that should have been addressed Table 3. Definition of technology readiness level for seismic accelerated bridge construction (SABC). Level Definition for Accelerated Bridge Construction 1 A design concept has been formulated. 2 The connection type has been analyzed or tested for static strength. 3 The connection type has been successfully deployed in a low seismic region. 4 The connection type has been analyzed for response to inelastic cyclic loading. 5 The critical connection components have been tested under inelastic cyclic loading. 6 A connection subassembly has been tested under inelastic cyclic loading. 7 Seismic design guidelines for the connection type have been formulated and published. 8 The connection has been used in a bridge constructed in a high seismic region. 9 The connection type has performed adequately during a design-level seismic event in the field.

OCR for page 9
11 Table 4. Evaluation of technology readiness level of connection types and identification of knowledge gaps. Technology Readiness Level (TRL) % of Development Complete TRL Description 0-25 25-50 50-75 75-100 1 Concept exists 2 Static strength predictable 3 Low seismic deployment 4 Analyzed for seismic loading 5 Seismic testing of components 6 Seismic testing of subassemblies 7 Design and construction guidelines 8 Deployment in high seismic area 9 Adequate performance in earthquake in earlier stages. For example, for the development of a seismic struction of a CIP bridge bent, and then to do the same for four connection, it is unlikely that a non-seismic deployment per of the precast groups (socket, pocket, bar couplers, and grouted TRL 3 is conducted. Hence, constructability issues in the field ducts) used to construct a typical bent. The predicted time sav- cannot be recognized until deployment of the connection in a ings were then computed as the difference between the time seismic area at TRL 8. This seems to be a bearable risk. On the needed for the precast system in question and the CIP system. other hand, a risk might be perceived higher if a connection has The connections were evaluated by connection type, rather been deployed to a seismic area without TRL 6, seismic testing. than including every possible variant found in the appendices. The estimates were necessarily subjective and were influ- enced by the prevailing building culture in the state (drop cap Evaluation of Potential Time Savings beams and precast, prestressed concrete girders). However, and Performance of Connections efforts were made to minimize the subjectivity, first by arrang- To identify connection systems that merit further invest- ing the presence of both design and construction expertise ment in testing and analysis, two other measures were seen to at the meeting, and second by discussing each construction be necessary. In this report, they are called the "time savings step in detail, including possible adverse circumstances, before potential" and "performance potential." The first is a simple assigning an approximate time. Despite those efforts, slight measure that indicates the time savings that appear possible if regional variations must be expected for the estimated time the connection is used. The real time savings depends on the savings computed by this process. construction system in which the connection is incorporated, The second measure is a composite measure of the perform- so the evaluation is necessarily subjective and approximate. ance potential of the connection type and is defined in terms of However, it is a measure of the possible time advantage rela- the connection's construction risk, seismic performance, dura- tive to traditional CIP construction for the connection type. bility, and post-earthquake inspectability. The scale is given in The scale is given in Table 5. Table 6. To establish the time savings for each connection type, the To show good performance potential, a connection must be researchers convened a meeting attended by a bridge contrac- expected to score at least adequately in all four categories. A tor, a Washington State DOT construction engineer, two "much worse" score in any one indicates a potentially unsatis- Washington State DOT design engineers, and two researchers. factory connection type. If connections have "slightly worse" A detailed description of this is included in Appendix H. The scores in one or two categories, those scores could be offset by goal was to generate time estimates for each step of the con- better performance in other categories. However, outstanding performance in one category would not necessarily make the connection type more attractive than performance that is Table 5. Connection time savings potential. merely satisfactory. Thus, the scales should saturate. For exam- ple, if most structures might be expected to experience 1.5 to Time Savings Definition Potential Relative to CIP Value 2% drift demand during a major seismic event and drift capac- +2 Much better ity of 5% was considered "adequate," then a connection drift +1 Slightly better capacity of 12% adds little to the value of the system because 0 Equal it is very unlikely to be used. This argument also applies to all -1 Slightly worse four categories. The construction risk evaluates the possibil- -2 Much worse ity that something might go wrong during construction and

OCR for page 9
12 Table 6. Connection performance potential. Seismic Performance Definition Construction Performance Durability Inspectability Potential Relative to CIP Risk Value Value Value Value +2 Much better +1 Slightly better 0 Equal -1 Slightly worse -2 Much worse detract from the quality or schedule. However, it does not typical ABC practice. The ratings are presented in Table 7. The measure the potential time savings so it is also measured using following issues are considered: a scale that saturates. The performance evaluation is somewhat subjective, as it is Complexity of detailing and number of parts based on the knowledge of the individual research team mem- Required construction tolerances during component bers in combination with the information gathered as part of fabrication and field installation this project. No additional studies or calculations have been Handling, lifting, and shoring equipment needed for field performed to support any individual evaluation. However, installation where the need for such further studies is recognized, sugges- Difficulty of labor access, work environment, and work tions are given in the report. Because the performance poten- condition tial is a qualitative measure, the scale was deliberately kept Complexity of installation procedure and number of steps simple. Each characteristic was defined relative to the corre- Vulnerability to construction mishaps, such as component sponding measure for CIP reinforced concrete construction. damage during handling and noncompliant procedures, In most cases, little information was provided by the respon- and availability of inspection and mitigation methods dents about durability and inspectability. Therefore, a default Sensitivity of installation schedule to individual operations, value of 0 (equal to CIP concrete) was used unless specific such as grouting and the time for grout to set information was available. Dependence on specialty trades or parts It should be noted that some interaction exists between the Repetitiveness of work and learning curve TRL and the performance potential. If the connection type has Risks associated with subcontracting part of the work already been developed to a high level, much will be known about its performance. The performance potential value can, Definition of Seismic Performance Rating Criteria therefore, be based on objective facts rather than subjective estimates. The seismic performance rating evaluates how an ABC con- The measures of potential time savings and performance nection for a specific seismic performance strategy, per Table 1 could be combined to simplify the evaluation procedure. How- (CP, ED, and DE), performs compared with a CIP connec- ever, doing so would fail to display the relationship between tion for a specific seismic zone (low, moderate, and high). risk and reward. For example, the same value might be assigned The criteria are defined in Table 8. The following issues are to one connection type that offered the potential for large time considered: savings (if everything went right) but carried a high risk of something going wrong and to a second connection type with Are there experimental data available and do they demon- little potential time savings and little risk. To preserve this strate a cyclic loading behavior that is comparable to CIP important distinction, the two characteristics were evaluated construction? separately. Is the connection emulating CIP construction with proper The individual performance evaluation criteria are defined seismic detailing? in the following paragraphs. Is it possible to develop bar strength, as necessary, for cyclic loading? Is it possible to prevent excessive concrete spalling? Definition of Construction Risk Rating Criteria Is it possible to prevent bar buckling? The evaluation of the construction risks of a connection col- Does the connection allow strain penetration under inelas- lectively assesses the difficulty to fabricate and install a con- tic loading? nection and the associated quality, cost, and schedule risk for Are bars spliced outside the plastic hinge zone?

OCR for page 9
13 Table 7. Rating for construction risk. Risk Definition Potential Relative to CIP Description of Field Work Construction Risk +2 Much Better Detailing is simple and can be done by a reduced There is a very high likelihood construction crew with minimum need for large that a connection will meet the construction equipment. required quality standard, cost, and installation schedule. +1 Slightly Better Detailing is simple and fabrication and installation There is a high likelihood that a of components can be performed by typically connection will meet the skilled construction workers under predictable required quality standard, cost, conditions using conventional construction and installation schedule. equipment. 0 Equal Detailing is simple but requires attention to fit-up There is a high likelihood that a and appropriate use of materials. Reasonably connection will meet the common supervision is required. Fabrication and required quality standard, but installation of components might require a specialty there is a minimal risk for not contractor or specialized equipment. Most meeting installation cost or contractors will be able to successfully construct schedule. the project. 1 Slightly Worse Detailing is somewhat complex, but skilled There is a minimum likelihood construction workers can execute the construction. that a connection will not meet The work, while complex, is not out of the the required quality standard experience range of a skilled crew but might lead to without repairs after initial a slow learning curve, with attendant mistakes, for construction and there is a an inexperienced one. The work might involve moderate risk for not meeting specialty contractors or specialized equipment. installation cost or schedule. Close control will be needed to ensure appropriate quality and final acceptance. 2 Much Worse Detailing is complex and skilled construction There is a moderate likelihood workers under close supervision will be required to that some repairs may be properly execute the construction. Specialty required after initial contractors or specialized equipment will most construction to satisfy the likely be required for installation work. Tolerances acceptance criteria for the work may be close, materials may be difficult to use in and there is a high likelihood the construction, and tight controls over the work that the connection will not must be worked out in advance and specifically for meet the cost or installation the particular project. Mock-ups would typically be schedule. beneficial and potentially required. Only the most experienced contractors will be successful with execution of the work. Is it possible to retain axial and shear capacity during cyclic Does the connection provide adequate deformability and loading? strength for its intended seismic performance strategy? Is the connection self-centering after cyclic loading? Can damage be contained to the plastic hinge region? Definition of Inspectability Rating Criteria Does the connection have a potential for energy dissipation similar to CIP? The inspectability rating focuses on post-earthquake inspec- tion of the seismic connection elements. It considers the abil- ity to recognize damage by visual inspection and whether there Table 8. Definition of seismic performance are methods available for damage assessment of the critical potential. structural components, such as reinforcement and post- tensioning. The rating directly compares to how difficult it Seismic Performance would be to inspect and assess damage of the same connection Potential Definition Relative to CIP +2 Much Better built in CIP or CIP-emulative precast concrete. The rating is +1 Slightly Better presented in Table 9. The following issues are considered: 0 Equal 1 Slightly Worse Can an inspector conclude that there is no damage if no 2 Much Worse damage is observed by visual inspection?