Recent Developments in the Design of Grouted Connections

ABSTRACT A major research project has now been completed into the structural behaviour of grouted pile/sleeve connections. This covered static strength, the effect of cyclic movement during grout setting, long term fatigue, calibration of measured strengths for different quality control samples and the investigation of connections removed after 13 years service in the North Sea. Preliminary data from this project resulted in the issue of revised Guidance Notes - by the UK Department of Energy and have been recognised in recent amendments to API RP2A. -The purposes of this paper are to disseminate test results not previously published, to compare and discuss the provisions of the latest design codes in relation to the available data and to discuss the implications for design. The result and discussions apply to all types of grouted connections and many types of structures, including pile/sleeve connections for fixed jackets and tension leg platforms and grouted connections used for repair of tubular structures. Results are included for early age cyclic loading tests, long term fatigue tests and comparative strength tests for 2in, 3in and 4in cubes and cylinders. The findings from a comparative study' of design guidance from API and UK Department of Energy against the test database is given for static strength. The paper notes that considerable care is required in the interpretation of and generation of guidance from test data for grouted connections. Many parameters affect the construction and performance of such connections and these must be brought to the attention of designers if necessary safety margins are to be maintained. INTRODUCTION Grouted pile/sleeve connections are a critical element of offshore structures, especially for deeper water fixed platforms and sea bed templates where piles terminate below sea level and welding of pile to sleeve is not possible. The concept is also used extensively for repair and strengthening applications for both jacket members and joints. This paper presents an outline of the results of a major research project undertaken with UK Department of Energy funding and also comments on the latest provisions of design codes which have recognised this research effort. A complete dissertation on the research programme is given in Reference 1. SCOPE OF RESEARCH PROGRAMME The requirement for a parametric study of grouted connections was established in 1977. Some previous work had identified the substantial improvements in connection strength that can be obtained by using shear connectors and indicated the major geometrical and material properties which affect strength; these data were used to assist in programme definition. The project was carried out between 1978 and 1981 in five phases, as listed below. This paper is concerned with Phases I to IV.Phase I Static strength tests (see below)Phase II Early age cyclic loading testsPhase IIILong term fatigue testsPhase IV Measurement of grout compressive strengthPhase V Static tests on connections recovered from a decommissioned North Sea Structure