Development of drift design model for high‐rise buildings subjected to lateral and vertical loads

Recent developments of resizing algorithms based on displacement participation factor have had a significant impact on drift design of high‐rise buildings. However, most drift design methods based on resizing algorithms have considered only lateral load and overlooked the effect of the vertical load in the calculation of member displacement participation factors. Therefore, in this paper, the practical drift design method of high‐rise buildings is presented in the form of a resizing algorithm by developing product integral modules required for the calculation of displacement participation factors with the consideration of both lateral and vertical loads. The effect of vertical load on the drift design model based on member displacement participation factors is investigated in detail using the verifying example of a 20‐story building structure. The drift design method in combination with the strength design module is then applied to the drift design of a 60‐story high‐rise building structure. Copyright © 2007 John Wiley & Sons, Ltd.     

A simplified method for instability and second‐order load effects of framed structures: Story‐based approach

Several building codes such as ANSI/AISC 360‐16 and EC3 EN 1993‐1‐1 require the use of a proper design method to consider instability and second‐order load effect problems for individual system elements and the entire structural system. Various methods are available to assess stability. All of these methods should consider P‐Δ and P‐δ effects (second‐order effects). The following calculation procedures are presented in this study: (a) a simplified method is developed for P‐Δ and P‐δ analysis in regular frames under the effect of constant axial loads to obtain story drifts and end moments; (b) this method can be applied to an entire building or any individual story, that is, story‐based design is possible; and (c) column effective length factors are obtained for individual columns. In addition, design tables are presented.     

Load resistance and hysteretic response of rhombic grid hyperboloid‐latticed shell subjected to combined vertical and horizontal loads

A new type of rhombic grid hyperboloid‐latticed shell (RGHLS) being investigated in this study is only formed by major and secondary inclined columns without any circumferential hoop members. This intends to achieve more transparency for architectural effect by neglecting its circumferential hoop members and lateral braces in radial direction of the RGHLS, and meanwhile, the RGHLS is expected to experience a significant strength reduction. This paper numerically investigates the load resistance and hysteretic response of such RGHLS subjected to combined vertical and horizontal loads by adopting finite element method, where multicolumn interaction instability failure mechanism and load‐carrying capacity of the RGHLS are being focused on. It was found that the RGHLS failed by multicolumn interactive instability between the major and secondary columns, with associated in‐plane and out‐of‐plane flexural deformations of the columns. The overall interactive load‐carrying capacity design curve N/Nu‐M/Mu of the RGHLS was proposed based on numerous finite element results. The results indicate that the strength design of the RGHLS with a door opening being adopted in the practical engineering application is reliable and rational with a certain amount of safety margin. At last, hysteretic response of the RGHLS is investigated according to the loading protocol specified in AISC341‐05.     

Experimental and analytical investigation on seismic behavior of Q690 circular high‐strength concrete‐filled thin‐walled steel tubular columns

This paper proposed a new Q690 circular high‐strength concrete‐filled thin‐walled steel tubular (HCFTST) column comprising an ultrahigh‐strength steel tube (yield strength f_y ≥ 690 MPa). A quasi‐static cyclic loading test was conducted to examine the seismic behavior, and the obtained lateral load‐displacement hysteresis curves, skeleton curves, and ductility were analyzed in detail. Then, a numerical model based on a nonlinear fiber beam‐column element incorporating the modified uniaxial cyclic constitutive laws for concrete and steel was developed mainly to predict the seismic behavior of the tested Q690 circular HCFTST columns. The effects of the concrete cylinder compressive strength (f_c), steel yield strength (f_y), axial compression ratio (n), and diameter‐to‐thickness (D/t) ratio on the seismic behavior were investigated through a parametric study. Finally, a simplified hysteretic model incorporating the moment‐resisting capacity and deterioration of the unloading stiffness in addition to a normalized skeleton curve and hysteretic criterion was established. The results indicate the following: the proposed Q690 circular HCFTST columns can display reasonable hysteretic behaviors to some extent; the use of high‐strength steel can lead to a significantly larger elasto‐plastic deformation capacity and delay the appearance of post‐peak behavior, even if a lower ductility capacity is provided; moderately loosening the limitations on the D/t ratio can also result in ideal hysteretic behaviors; and the established numerical model and simplified hysteretic model can satisfactorily predict the experimentally observed load‐displacement hysteretic curves, including the deterioration of the strength and stiffness and can, thus, offer design references for the elasto‐plastic analysis of circular HCFTST columns.     

高层建筑施工附着整体升降钢管脚手架的设计计算

附着升降脚手架涉及脚手架、钢结构、机械、电气和自动控制等技术领域,是一项具有综合性和复合性的施工机具和专项技术。附着升降脚手架的设计计算包括主要承重结构和升降设备、吊具、索具分别在使用、升降和坠落三种工况条件下的设计计算。作为推荐,给出主要承重结构按概率理论为基础的极限状态设计方法的基本表达式,明确各关键系数的取值,列表给出两种荷载附加计算系数的取值方法。还给出各主要构件的强度、刚度、稳定、抗倾覆的验算方法,并指出架体构架(即脚手架架板部分)与其他主要承重结构计算的不同特点。对升降结构中的升降设备、吊具、索具的设计,建议按容许应力设计法进行计算。     

Einsparpotentiale bei Tragkonstruktionen von Offshore‐Windenergieanlagen

Savings potential for support structures of offshore wind turbines. Due to the high ratio of dynamic loads from wind and wave forces on offshore wind turbines, the fatigue design analysis proves to be the determining factor for the dimensioning of support structures. As a result, the current design practice is limited, particu‐larly with regard to the economic benefits of employing high strength steels. Especially from the aspect of mass production, however, the economic optimization of the components is a sub‐stantial economic advantage for the companies. This paper presents different options for savings in the design and assessment of offshore‐foundation structures and provides the example of a transition piece for a jacket foundation structure. Savings potential is realized through optimal construction design, directionally dependent load determination, a refined methodology of analysis, as well as through modern methods of post weld treatment.     

Determinants of house dust,endotoxin, and β‐(1→3)‐D‐glucan in homes of Danish children

Little is known about the geographic variation and determinants of bacterial endotoxin and β ‐(1,3)‐d ‐glucan in Danish house dust. In a population of 317 children, we: (i) described loads and concentrations of floor dust, endotoxin, and β‐(1→3)‐d ‐glucan and (ii) their correlations and (iii) assessed their determinants; (iv) Finally, we compared our findings with previous European studies. Bedroom floor dust was analyzed for endotoxin content by the kinetic limulus amoebocyte lysate assay and for β‐(1→3)‐d ‐glucan by the inhibition enzyme immunoassay. The parents answered questions regarding potential determinants. We found: geometric means (geometric standard deviations) 186 mg/m² (4.3) for dust; 5.46 × 10³EU/m² (8.0) and 31.1 × 10³EU/g (2.6) for endotoxin; and 142 μg/m² (14.3) and 0.71 × 10³ μg/g (7.3) for β‐(1→3)‐d ‐glucan. High correlations (r > 0.75) were found between floor dust and endotoxin and β‐(1→3)‐d ‐glucan loads, while endotoxin and β‐(1→3)‐d ‐glucan concentrations were moderately correlated (r = 0.36–0.41) with the dust load. Having a carpet was positively associated with dust load and with endotoxin and β‐(1→3)‐d ‐glucan concentrations. Pet keeping, dwelling type, and dwelling location were determinants of endotoxin concentrations. No other determinants were associated with β‐(1→3)‐d ‐glucan concentrations. Compared with other European studies, we found lower β‐(1→3)‐d ‐glucan loads and concentrations but higher endotoxin loads and concentrations suggesting a geographically determined different composition of Danish floor dust compared with other European regions.     

Strain gradient effects on flexural strength design of normal‐strength concrete beams

In the flexural strength design of normal‐strength concrete (NSC) beams, the resultant concrete force and its centroid within the compression zone is generally expressed in an equivalent rectangular stress block. The equivalent concrete stress is expressed as , where is the uni‐axial concrete cylinder strength. Currently, the value of α stipulated in various design codes for NSC is taken as 0.85. Nonetheless, in an experimental study conducted earlier by the authors on NSC columns subjected to concentric and eccentric axial loads, it was found that the value of α significantly depends on strain gradient, which generally increases as strain gradient increases until it reaches a maximum value. Therefore, strain gradient is a critical factor and should be considered in the flexural strength design of NSC members. In this paper, a new flexural strength design method that incorporates the effects of strain gradient is developed for NSC beams. An equivalent rectangular concrete stress block, which is strain‐gradient dependent, is proposed and applied to produce a set of equations for the flexural strength design of singly and doubly reinforced NSC beams with various concrete strengths. Lastly, these equations are converted into charts for practical design application. Copyright © 2010 John Wiley & Sons, Ltd.     

Measured and Predicted Loads in Multi-Anchor Reinforced Soil Walls in Japan

More than 3000 multi-anchor walls have been built in Japan over the last decade. The paper briefly reviews a total of eight instrumented wall sections that can be used to estimate anchor loads at the end of construction. Measured loads are compared to predicted values using equations found in current design guidelines. The comparison shows that the current Japanese and UK design methods to compute anchor loads are reasonably accurate for walls with frictional backfills provided K_a is calculated using the Rankine equation. For walls with cohesive-frictional backfills, current design methods over-predict anchor loads by as much as a factor of two. The eccentricity term in current UK and Hong Kong design methods is shown to not improve the accuracy of load predictions and it is recommended that this additional complexity be removed from these equations. A new load equation is proposed and constant coefficients are back-fitted to measured anchor load data. The new method is demonstrated to give quantitatively better predictions of anchor loads based on the statistics for load bias values computed as the ratio of measured to predicted anchor loads at the end of construction.     

Design method for checking tensile stresses under service loads in cracked prestressed concrete members with 2,400‐MPa strands

The ACI 318‐14 building code requirements specify that the net tensile stresses of prestressing strands under service loads (Δf_ps ) shall be limited to 250 MPa for proper crack control of prestressed concrete (PC) members which are classified as Class C. However, as high‐strength prestressing strands with a tensile strength of 2,400 MPa have recently been developed and applied to PC members, this requirement needs to be reviewed. In this study, experiments and analysis were carried out in order to investigate the Δf_ps of PC members with the recently developed 2400 MPa strands, and in the test, the strain distributions, flexural crack widths, and stress change in bonded prestressed reinforcement were measured in detail according to the applied loads. In addition, the minimum magnitudes of effective prestress to satisfy the stress limitation of the net tensile stress of prestressing strands specified in the current design code were estimated using a nonlinear flexural analysis model, and a simplified design equation was proposed for a simple calculation of the Δf_ps at the design stage.     

Overstrength and force reduction factors of multistorey reinforced‐concrete buildings

This paper addresses the issue of horizontal overstrength in modern code‐designed reinforced‐concrete (RC) buildings. The relationship between the lateral capacity, the design force reduction factor, the ductility level and the overstrength factor are investigated. The lateral capacity and the overstrength factor are estimated by means of inelastic static pushover as well as time‐history collapse analysis for 12 buildings of various characteristics representing a wide range of contemporary RC buildings. The importance of employing the elongated periods of structures to obtain the design forces is emphasized. Predicting this period from free vibration analysis by employing ‘effective’ flexural stiffnesses is investigated. A direct relationship between the force reduction factor used in design and the lateral capacity of structures is confirmed in this study. Moreover, conservative overstrength of medium and low period RC buildings designed according to Eurocode 8 is proposed. Finally, the implication of the force reduction factor on the commonly utilized overstrength definition is highlighted. Advantages of using an additional measure of response alongside the overstrength factor are emphasized. This is the ratio between the overstrength factor and the force reduction factor and is termed the inherent overstrength (Ω _i). The suggested measure provides more meaningful results of reserve strength and structural response than overstrength and force reduction factors. Copyright © 2002 John Wiley & Sons, Ltd.     

A displacement‐based strength reduction factor for high‐rise steel moment‐resisting frames

A preliminary study of the ‘displacement‐based strength reduction factor’ for high‐rise steel moment‐resisting frames is presented in this paper. The base shear capacity required for a high‐rise steel building in a displacement‐based design can be estimated from the reduction of the displacement‐based elastic response. The conventional force‐based design procedure is still adopted as the initial stage of the displacement‐based design. To establish an empirical formula of the proposed displacement‐based strength reduction factor, non‐linear time‐history analyses of six moment‐resisting frames are investigated. The conventional ‘equal displacement rule’ and ‘equal energy rule’ are no longer held when the displacement limitations are considered. As a result, a modification for conventional strength reduction factors is proposed for further applications in displacement‐based design. An adjustment factor defined as ‘deformation energy ratio’, β, which is related to natural periods, is introduced. The final displacement‐based strength reduction factor is defined as a function of ductility demand, fundamental period and the deformation energy ratio. Copyright © 2006 John Wiley & Sons, Ltd.     

Concurrent flexural strength and ductility design of RC beams via strain‐gradient‐dependent concrete stress–strain curve

The authors have previously conducted an experimental study that showed that strain gradient would improve the maximum concrete stress and strength of reinforced concrete (RC) members under flexure. As a continued study, the authors herein will extend the investigation of strain gradient effect on flexural strength and ductility of RC beams to higher strength concrete up to 100 MPa by theoretical analysis. In this study, the flexural strength of RC beams is evaluated using nonlinear strain‐gradient‐dependent stress–strain curves of concrete applicable to both normal‐strength and high‐strength concrete. On the basis of this, a parametric study is conducted to investigate the combined effects of strain gradient and concrete strength on the flexural strength and ductility of RC beams. It was evident from the results that both the flexural strength and ductility of RC beams would be improved with strain gradient considered. From the results, two formulas are proposed for the strain‐gradient‐dependent concrete stress block parameters α and β. A constant value of 0.0032 is proposed for the ultimate concrete strain in flexural strength design with strain gradient effect considered. Lastly, for practical engineering design purpose, design formulas and charts have been presented for flexural strength and ductility of RC beams incorporating strain gradient effect. Copyright © 2015 John Wiley & Sons, Ltd.     

Hygrothermische Beanspruchung und Lebensdauer von Wärmedämm‐Verbundsystemen

Hygrothermal loads and service life of external wall insulation systems. Service life and aging behaviour of external wall systems depend on their hygrothermal loads. Apart from the fluctuating climatic conditions temperature, solar radiation and humidity there are often additional exterior or interior sources of moisture, e.g. driving rain, construction moisture or surface condensation acting on facades. External wall insulation systems (ETICS = E xternal T hermal I nsulation C omposite S ystems) are especially affected due to their low mass. However, the long‐term observation by repeated inspections of the same objects over a period of 30 years proves that ETICS show not more damage than traditional facades. Apart from minor esthetical problems due to soiling or microbial growth their long‐term behaviour is very encouraging. Maintained at normal intervals ETICS are as durable as traditionally rendered masonry walls.     

Bemessungsvorschlag für Holz/Beton‐Verbundbalken unter Beachtung abgestufter Verbindungsmittelabstände

Design proposal for timber/concrete composite beams with graded connnector distances. The distance of connections of timber/concrete composite beams is often graded for economical reasons according the shear force distribution. The load‐carrying capacity of composite beams according to DIN 1052 respectively E DIN 1052 with internal forces, which are linearly determined, (γ‐procedure) are clearly reduced compared to beams without graded distances of connectors. The actual load‐bearing behaviour distinctly shows non‐linearities. The influence of the gradations of the connectors on the load‐bearing behaviour of composite beams is investigated, because the influence of the stiffness of connections on the load‐bearing capacity of composite beams is small. The paper presents a comparison between failure loads determined by FE‐analysis and the working loads according to the current design rule. It is shown that the decrease of load‐bearing capacity is smaller than assumed by current code of practice. Structures with several different distances of connections have the largest safety‐factor. These systems can more economically be designed. As the result of the investigations, a new design proposal is presented, which takes non‐linearities into account and guarantees a constant safety‐zone between failure load and working load. These proposal permits an economic design of timber/concrete composite beams.     

机械结构静强度可靠性设计中的载荷测试

本文从随机理论出发，提出了对样机进行载荷实测及数据处理并获得极值载荷主要概率特征的方法。首次对叉车门架进行了载荷和极值载荷统计处理，所得数据可直接用于叉车门架静强度可靠性设计。     

Analytical compressive stress–strain model for concrete confined with high‐strength multiple‐tied‐spiral transverse reinforcement

The behavior of reinforced concrete members subjected to seismic loads is mainly based on the ultimate strength of concrete and its ductility. Based on this, an additional configuration of transverse reinforcement using high‐strength multiple‐tied‐spiral was proposed to improve the strength and ductility of concrete. In this paper, an experimental study of a number of axial loading tests on reinforced concrete columns confined with high‐strength multiple‐tied‐spiral transverse reinforcement is described. The effects of spacing of circular spiral and rectangular hoop, the confined area of circular spiral and concrete strength on axial behavior of confined concrete were investigated. The formulas of confined compressive strength and corresponding axial strain, factor to control the slope of descending branch, and stress in high‐strength circular spiral at confined strength are proposed based on the test results. A stress–strain model is also proposed that is found to give reasonably good prediction of the experimental behavior of reinforced concrete (RC) columns confined by high‐strength multiple‐tied‐spiral transverse reinforcement.     

Bemessung von Dübeln am Bauteilrand unter Querlast: Ingenieurmäßiger Ansatz zur Berücksichtigung der Lastrichtung

Design of Anchors close to an Edge under Shear Loads Engineering Approach for Consideration of the Load Direction A universally valid proposal is made for the design of anchors close to an edge under shear loads for concrete edge failure. The angle of the shear load is taken into account during determination of the load distribution on each anchor of a group. Thus the model may be used for applications without and with hole clearance and for shear loads as well as for torsion moments.     

Evaluation of behavior factor of tunnel‐form concrete building structures using Applied Technology Council 63 methodology

Tunnel‐form construction system is used for buildings made up of slabs and walls. This system has represented fast construction technique, low cost and time saving in the construction period. However, there are no special requirements for seismic design of this type of buildings, and some provisions of the concrete bearing wall system are used. None of the seismic codes addresses the R factor for tunnel‐form buildings directly, and some doubts remained about prediction of the fundamental period. Meanwhile the force‐based methods, which depended on R factor and fundamental period, are still used for seismic design of this type of buildings. There is a need for evaluating the R factor for tunnel‐form buildings. The methodology was developed by the Applied Technology Council (ATC) entitled ATC‐63 Project for quantifying building system performance and response parameters for use in seismic design. Here, this methodology is used to estimate more reliable R factor for tunnel‐form buildings. An experimental program was carried out to decrease the uncertainty of finite element modeling and using it as a part of the methodology. A database was created, and some analyses were performed. The results of analysis were summarized to propose more accurate R factor for tunnel‐form buildings. Copyright © 2011 John Wiley & Sons, Ltd.     

Reliability-based calibration of load duration factors for timber structures

The load bearing capacity of timber structures decrease with time depending on the type of load and timber. Based on representative limit states and stochastic models for timber structures, load duration factors are calibrated using probabilistic methods. Load duration effects are estimated on basis of simulation of realizations of wind, snow and imposed loads in accordance with the load models in the Danish structural codes. Three damage accumulation models are considered, namely Gerhards model, Barrett and Foschi’s model and Foschi and Yao’s model. The parameters in these models are fitted by the Maximum Likelihood Method using data relevant for Danish structural timber and the statistical uncertainty is quantified. The reliability is evaluated using representative short- and long-term limit states, and the load duration factor k_mod is estimated using the probabilistic model such that equivalent reliability levels are obtained using short- and long-term design equations. Time variant reliability aspect is considered using a simple, representative limit state with time variant strength and simulation of the whole life time load processes.