The use of a single set of outriggers equipped with oil viscous dampers increases the damping ratio of tall buildings in about 6-10%, depending on the loading conditions. However, could this ratio be further increased by the addition of another set of outriggers? Should this additional set include dampers too? To answer these questions, several double damped outrigger configurations for tall buildings are investigated and compared with an optimally designed single damped outrigger, located at elevation 0.7 of the total building's height (h). Using free vibration, double outrigger configurations increasing damping up to a ratio equal to the single-based optimal are identified. Next, selected configurations are subjected to several levels of eight ground motions to compare their capability for avoiding damage under critical excitations. Last, a simplified economic analysis highlights the advantages of each optimal configuration in terms of cost savings. The results show that, within the boundaries of this study, combining a damped outrigger at 0.5h with a conventional outrigger at 0.7h is more effective in reducing hysteretic energy ratios and economically viable if compared with a single damped outrigger solution. Moreover, double damped outrigger configurations for tall buildings exhibit broader display of optimal combinations, which offer flexibility of design to the high-rise architecture.

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PurposeConstruction duration is referred to as one of the most crucial success elements for a construction project along with quality and cost. Modelling construction duration supports decision making at the early stages of a project. Exploring the complex structure of construction duration is necessary; hence this forms a basis to develop a predictive model. Therefore the main aim of this study is to determine the subset of variables for a descriptive model that explains the most substantial part of the variation in construction duration.Design/methodology/approachSecondary data set which includes 1,695 observations with 30 quantitative and four qualitative variables was utilized. Multiple linear regression was employed to define the relationship between explanatory variables and construction duration. General procedure for variable selection was presented in detail for data sets that suffer multicollinearity and singularity.FindingsAnalysis indicated that gross external floor area and cost of construction works are the major variables for describing the construction duration. In addition, categorisation with respect to type of facility, project location, availability of construction area, and market conditions was justified to be statistically significant.Research limitations/implicationsThe study was limited to the population: German building industry. Besides, the affect of various qualitative variables, identified in the literature, could not be assessed due to lack of data availability.Originality/valueTo the authors' knowledge, the study is the first to assess construction duration for German building projects. Moreover, it provides a method for describing variable selection routine transparently.

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The paper describes the main features of the 1999 edition of Fidic’s Red Book, possibly the most commonly used standard-form construction contract in international projects. The paper is addressed to construction professionals who already have an understanding of English construction contracts but have not yet looked into Fidic contracts. The 1999 Red Book is for use when the contractor has been given the design by the employer. The contract features general and particular conditions, the latter of which have to be drafted by the parties before the contract is entered into. A typical feature of the 1999 Red Book is the role of the engineer. Whether he has to act for the employer or whether he has to make a fair determination depends on the matter in question. There are two striking differences from the contract JCT SBC 2005 regarding claims of the contractor. First, only the 1999 Red Book contains strict time bars. Second, the clauses which contain events that justify claims are spread out over the whole contract and not contained in comprehensive lists of events. New features are clause 13.2 on value engineering and clause 20 on the impartial dispute adjudication board.