Outrigger Trusses Research Articles

Analysis of RCC Framed 45 Storey Building Using Different Combination of Outriggers

In this modern age of civil engineering, the construction industry has embraced a notable inclination towards erecting towering structures, with skyscrapers emerging as integral components of urban development. This trend presents a multifaceted challenge, not only for architects but also for structural engineers, who must ensure these high-rise edifices possess a robust design foundation capable of withstanding diverse loads and their combinations. While both wind and seismic forces exert significant pressures on tall buildings, the former often takes precedence due to its higher magnitude and frequency. Consequently, the structural design of high-rise buildings necessitates careful consideration of gravity, wind, and seismic loads. This study delves into the behaviour of reinforced concrete (RC) framed high-rise buildings (comprising 45 stories) augmented with outrigger truss systems constructed from both concrete and steel bracings. By exploring various configurations of outrigger placement, the aim is to mitigate structural deflection and compare the efficacy against conventional RC systems, both with and without shear walls.

Gaussian cross-entropy and organizing intelligence for design optimization of the outrigger system with inclined belt truss in real-size tall buildings

This research explores the optimal structural design for tall buildings with an outrigger and belt truss system. The study employs Gaussian Cross-Entropy with Organizing Intelligence (GCE-OI), a novel optimization approach that utilizes a self-organizing map as a machine learning algorithm, and Gaussian probability distribution in Cross-Entropy optimization. This approach is used to predict promising solutions and to guide the search process for swift convergence. The optimization encompasses member sizing (weight) and outrigger placement (topology) while introducing inclined belt trusses alongside traditional horizontal trusses for enhanced performance. The process involves optimizing a 25-story real-size model subjected to wind load, and the results are compared against multiple well-known algorithms. The results show that the proposed optimizer, supported by machine learning, outperforms alternative algorithms, offering superior solutions with enhanced convergence. Considering the efficiency of the inclined belt trusses and the proposed robust optimization method (GCE-OI), the optimally-placed outrigger system minimizes the constructional cost and enhances structural stability by limiting the responses.

A seismic behavior of RCC high rise structure with and without outrigger and belt truss system for different earthquake zones and type of soil

In the present era, there is more demand for high-rise buildings. The growing de- mand for high-rise buildings brings new difficulties and comes up with new safety precautions. With an increase in height of the structure, its rigidity reduces, making it difficult to withstand earthquake and wind effects, hence some preventative structural systems must be used. Some of them are bracings, shear walls, outrig- ger systems and belt truss systems etc. The outrigger and belt truss system is investigated in this study since it is the most effective method for high-rise buildings and skyscrapers. To prevent story drift and the rotational action of the core caused by seismic and wind forces, the external columns in an outrigger system are attached to the main inner or outer core using outrigger beams, walls, and trusses etc. at various floor levels. All external columns that are situated at the peripheral are connected together with truss elements in a belt truss system. This study investigates the comparison of the behavior of high-rise buildings with and without an outrigger system, and belt truss system for all seismic zones (zone II, III, IV and V) with different types of soil (hard, medium, soft). This study is carried out for 40 story buildings using response spectrum analysis. Analysis of the building is carried out by using ETABS 2018 software. The results are in the form of seismic responses like storey displacement, Storey drift, base shear are studied. Results show that the provision of an outrigger and belt truss system reduces the story displacement of the structure. After analysis and comparing the seismic responses of the structure, the building provided with the combination of outrigger and belt truss system perform better as compared to the only outrigger and belt truss system.

Influence of outrigger truss system on the seismic fragility of super high-rise braced mega frame-core tube structure

The braced mega frame-core tube (BMFCT) structure is an efficient seismic structural system for super high-rise buildings of over 500 m high. The outrigger truss (OT) system has become a commonly adopted design option for the super high-rise BMFCT structure, however, its influence on the seismic performance is not clear. In this study, the seismic responses and collapse risks of the 590-m-high BMFCT structures with and without OT system were analyzed. An efficient elasto-plastic modeling method was introduced to establish the accurate FE models. Based on the incremental dynamic analysis-based (IDA) fragility analysis, the deformation responses, energy dissipations, collapse risks and collapse resistance capacities, etc. were researched. The results indicate the average top displacements under earthquakes of ‘one-degree-higher’ rare intensities are reduced by the OT from 1286.51 mm to 1348.31 mm by 4.6%. The OT system can effectively limit the story drift ratios of the BMFCT under earthquakes with the lower intensity. With the increasing seismic intensity, the OT presents an unfavorable effect on the lateral deformations. The OT system increases the proportion of damping energy dissipation from 68.28% to 70.24%, and decreases that of plastic deformation energy dissipation from 20.74% to 20.12%, both by less than 2%. The OT system causes the slope of IDA curves to rise first and then fall, which is the opposite of that without OT. The OT system is detrimental to the structural collapse resistance capacity, reducing the collapse margin ratio from 8.46 to 7.41 by about 14%. The OT's function can effectively reduce the cross-sectional dimensions of main components and ensure the architectural functionality and view-transparency. In the seismic design of BMFCT structures, the OT system should be given more attention, especially in the earthquakes stronger than rare intensity, and recommended to be designed to meet the basic structural stiffness requirement and not to provide excessive lateral stiffness resistance.

Performance-Based seismic design and evaluation of out-of-code structure on Nanjing Financial City

The main scope of performance-based seismic design and evaluation study focuses more on the seismic performance of the simple structure or the regular structure, instead of out-of-code structure. The C1 tower in Nanjing Financial City is taken as an engineering case study. Many design indexes of the original design scheme of the structure exceed the requirements of the existing Chinese specifications, such as the height exceed the limits, the torsional irregularity, the partial floor slab discontinuity etc., which are summarized in detail in this paper. Then, several special structural design strategies are adopted to improve the overall seismic performance of this out-of-code structure. For example, multiple lines of seismic defences are set and the outrigger trusses are strengthened to solve the height overrun. For torsion irregularity, the influence of the bidirectional seismic torsion effect is considered in the calculation. Finally, according to the results of dynamic elastoplastic time history analysis under rare earthquakes, the seismic performances of the out-of-code structure are evaluated in detail. The analysis results show that the overall seismic performances of the structure are all within a reasonable range, and the seismic performance of the main components in the structure all meet the specification requirements.

Shaking table test and seismic behavior of Ningbo Hengda Tower

SummaryA super tall building named Ningbo Hengda Tower is located in Ningbo City, China. It has 91 stories with a total height of 450 m. The structure system of the building consists of three parts, that is, the reinforced concrete core, the outer frame system, and the outrigger trusses connecting the core wall and outer frame. The unique outer frame system is spindle shaped with oblique columns. The outrigger trusses are located at three different levels above the ground, thus strengthening the building and creating irregularities in the stiffness of the structure along the building height. Great challenges are existed in seismic design and analysis of the building. Shaking table test was carried out for a 1/40 scaled model of the building under a series of different base excitations with increasing amplitudes. The dynamic properties, seismic responses, and failure mechanism of the structure are investigated. Test results show that the structure behaved well under designed level earthquakes. The weak points of the structure are identified based on visible damage of the tested model, and some suggestions are made for the improvement of the seismic behavior of the building. It is suggested that measures be taken to improve the ductility of the building from floor 71 to floor 79 and the adjacent floors.

Review on High Rise Building with Outrigger and Belt Truss System

Abstract: In present era there is more demand of high rise building. The growing demand for high-rise buildings brings new difficulties and comes up with new safety precautions. With increase in height of structure its rigidity reduces, making it difficult to withstand with earthquake and wind effects, hence some preventative structural systems must be used. Some of them are bracings, shear wall, outrigger system and belt truss system etc. The outrigger and belt truss system is investigated in this study since it has been found to be the most effective method for high rise buildings and skyscrapers. To prevent story drift and the rotational action of the core caused by seismic and wind forces, the external columns in an outrigger system are attached to the main inner or outer core using outrigger beams, walls, trusses etc. at various floor levels. All external columns that are situated at the peripheral are connected together with truss elements in a belt truss system. A number of studies on this subject that have been done in the past are reviewed in this paper. Reviewing research papers let us know about the conclusive results, which served as the basis for the objective of our future study. One of the best systems for controlling excessive drift and lateral displacement caused by lateral loads is the outrigger and belt truss system. By using this system, the risk of structural and non-structural damage can be reduced during small or medium lateral loads caused by either wind or earthquake load

Experimental study on seismic behaviour of the outrigger truss-core wall spatial joints with peripheral CFST columns

To understand the feasibility and seismic behaviour of the outrigger truss-core wall joints with peripheral concrete-filled steel tubular (CFST) columns, this paper presented an experimental study on outrigger truss-concrete shear wall joints under quasi-static cyclic loading. Two joint specimens with various details, namely, the length of the shear wall, were tested and intensively compared. The failure mode, load versus displacement hysteretic curve, strain distribution, failure mechanism and the key indexes reflecting the seismic behaviours, i.e., strength degradation, stiffness degradation, ductility and energy dissipation capacity of joints were analysed, respectively. The results show that the failure process of joints can be divided into three stages, namely, stress stages of shear wall and outrigger truss, outrigger truss and concealed column system, and failure stage of truss system, and the energy consumption of joints mainly occurs in the second stage. The failure of the two joints are located at the connection of outrigger truss and concealed column in shear wall. The length of wall has limited influence on the peak bearing capacity of joints, and the concentrated load of chord and web members of outrigger truss is transferred to shear wall through concealed column connection. The reasonable transition of stiffness of the connection between the shear wall and the outrigger truss should be adopted in the joint design, and the increase of the distance from the concealed column to the edge of the shear wall is beneficial to improve the mechanical performance and ductility of joints. The average ductility factor of two tested joints under the positive and negative loading is 1.67. The average value of the equivalent viscous damping coefficient of tested joints is 0.23, which is 130% higher than that of reinforced concrete joints of 0.1. These indicate that the tested joint exhibits a superior seismic performance and energy dissipation capacity.

A novel damped braced tube system for tall buildings in high seismic zones

SummaryThe damped outrigger system is known to efficiently provide additional damping in buildings with heights of over 250 m. However, particularly for supertall buildings in the center of Tokyo, Japan, the outrigger truss from the center core to the exterior columns need to span distances of more than 20 m. This increases the flexural stiffness demand on the outrigger that leads to larger truss depths making the damped outrigger system inefficient. For such tall buildings with large plans, a new damping modification system, the “damped braced tube system” is proposed, where the exterior surface of the elastic mega braces are partially removed vertically to create a split and are replaced with dissipaters (energy‐dissipation devices). The damped braced tube system enhances the seismic performance as the exterior surfaces of the elastic mega braces work together with the damped slits like in a coupled wall system and increases the overall damping ratio. In this paper, numerical models were constructed based on a real project in Japan consisting of a 397‐m supertall building employing the damped tubular braced system using oil dampers (referred to as viscous dissipaters). A series of generalized response spectrum based numerical analyses and optimizations were performed to minimize the seismic response. The proposed system exhibited improved damping performance with the first to third mode damping ratios reaching to more than 7% while providing a wide range of options for dissipater distribution for design. Finally, the elevation of the slit's base is recommended to be equal to 0.22 of the total building height considering the trade‐off relationship between the first modal damping ratio and the fundamental period.

Effect of outrigger systems for tall buildings

The development of tall building construction is increasing worldwide today to meet the demands and challenges in construction industry. The intention of tall building construction is owing to population growth and lack of enough horizontal spaces. The rise in height of the tall building needs at most care on lateral stiffness of the structure where the introduction of outrigger trusses plays a vital role. In this paper, an investigation has been performed to study the behaviour of outrigger trusses on different locations of the building using response spectrum analysis. For this analysis, a three-dimensional building model is developed for G + 20, G + 26 and G + 30 storey RC building to find out the performance of outrigger trusses subjected to earthquake loading conditions. The performance analysis is evaluated by ETABS software and the analysis results were compared among lateral displacements, storey shear and storey drift to find out optimal position of outriggers and an efficient reduction of storey drift in a structure. It was observed that, the introduction of outrigger trusses at the bottom storey reduces considerable drift to enhance the stiffness of the structure.

Comparative analysis of Wall Belt Systems, Shear Core Outrigger Systems and Truss Belt Systems on Residential Apartment

Abstract: The outrigger structural system is one of the horizontal load resisting systems. In this system the belt truss ties all the external columns on the periphery of the structure and the outriggers connect these belt trusses to the central core of the structure thus restraining the exterior columns from rotation. The shear wall was implemented to oppose lateral loads. To complete these characteristic the Outrigger & wall belt system used in the structure. In this project a G+10 Storey structure has analysed using seven different cases named as RA1 to RA7-OTB. 1 to 7 indicates single outrigger system, shear core outrigger system truss belt support system with optimized trusses, at various locations under seismic zone III. The built up area used for various case as 315 sq. m. After performing result analysis, the comparative analysis of all the cases shows that the most efficient case for the above study is Case RA4. Here for efficiency of the project, two types of optimized truss belt support which has performed well and observed as most optimized and correspondingly minimum in all the cases. Keywords: Truss wall belt support, core wall belt support, outrigger, wall belt, CSI-ETABS, multi-storey

Optimization of location of outrigger system in tall buildings of different aspect ratios

The dynamic behavior of tall building structures is unpredictable under lateral loads. The key concern of tall building design is controlling deflections under lateral loads like earthquake loads or wind loads. There are many structural forms to resist lateral loads; the outrigger system is one of the best structural forms for effective lateral load resistance in tall buildings. Since the location of the outrigger enormously influences the dynamic behavior of tall structures, the present research focused on finding the optimum location of the outrigger along with the height of the structures. For this contest, a numerical study is carried out with five structural models of different aspect ratios. The aspect ratio of the models considered is 0.91, 0.61, 0.45, 0.36 and 0.30. All five models are designed as per Indian codes, IS456, and IS1893. For the observation of the dynamic performance of the five models, the outrigger truss without any belt truss is placed at different heights of the building. For each position, the dynamic performance of the 3D structure is observed. The study is made to compare the reductions in displacements, inter-story drifts, and overturning moments for the buildings with and without outriggers. This study focus on the change of the position of the outrigger for greater resistance to lateral loads depending upon the aspect ratio of the buildings. The analytical results have been studied to find out the optimum location of the outrigger, along with the height of the structures with different aspect ratios. It was concluded that the optimum position of outrigger truss without belt truss is at 65 to 80% of the height of the building for aspect ratios between 0.45 and 0.95.

First mode damping ratio oriented optimal design procedure for damped outrigger systems with additional linear viscous dampers

The damped outrigger system is in widespread use as a damping modification system for tall buildings that provides high additional damping in addition to the bending back effect against the core. However, while the enhanced seismic performance of damped outrigger systems was confirmed in previous studies all over the world, a general-purpose optimal design method focusing on modal damping ratios has not been established yet. This paper proposes an optimal damper design kit composed of a first mode damping ratio oriented design policy, simple equations of optimal damper-connection stiffness ratio to maximize first mode damping ratio, a machine learning model to estimate first mode natural period and damping ratio. The tenability of the first mode damping ratio-oriented design policy was confirmed by performing complex modal analyses on single to quad damped outrigger systems incorporating linear viscous dampers and assigning realistic stiffness values to the outrigger trusses. The simple design equations of optimal damper-connection stiffness ratio and the machine learning model for first mode characteristics were developed based on a large number of analytical results. The proposed optimal design kit has been made available as a web application-based design tool.

Shaking table test of a supertall building with hinged connections connecting a gravity load resisting system to a lateral force resisting system

ABSTRACT Considering a common practical engineering structure, namely, a concrete-filled steel tube (CFST)-steel frame-core tube structure, the rigid connections between the steel beams and the columns/core are modified into hinged connections. In this manner, a 1:40 reduced scale specimen representing a real supertall building that consists of 68 storeys and four underground storeys is constructed for a shaking table test to study the seismic performance of the structure. Numerical simulations are performed to analyse the time history responses of a CFST-steel frame-core tube structural system with three different connection configurations: hinged joints, rigid joints and strengthened layers (which are defined as storeys equipped with outrigger and belt trusses to limit inter-storey drift). The results indicate that the earthquake damage to the structure mainly occurs in the lower storeys at the connections and the corners of the core tube. The seismic response of the structure under the long-period ground motion is significant. The largest inter-storey drift ratio of the core tube reaches 1/26, which exceeds the threshold of the frame-core tube structure system in the Chinese Code by a factor of 3.8. Both the rigid joints and the strengthened layers can reduce the inter-storey drift ratio of the structure.

Comparative study on the effect of outrigger on seismic response of tall buildings with braced and RC wall core. I: Optimum level and examining modal response spectrum analysis reliability

SummaryDesigners usually use modal response spectrum analysis (MRSA) in design of tall buildings. This paper studies the reliability of this technique in predicting real seismic behavior of tall buildings with outrigger and belt truss. Four tall buildings utilizing either braced or reinforced concrete shear wall core with 28 and 56 stories were designed as the base models according to current design codes. Outrigger and belt truss were added at quarters of the structure height generating 44 structural models. Results obtained from MRSA of these models are discussed and compared to those obtained from nonlinear time history analysis (NLTHA). It was observed that MRSA unrealistically overestimates beneficial effects of outrigger on drift reduction of tall buildings with braced core. NLTHA showed that the maximum lateral displacements of the structures with braced core are less than those of buildings with RC shear wall, but they experience more residual displacements. Adding outrigger could reduce maximum lateral displacement of buildings with RC shear wall core (in excess of 30%) but had minor effect on this index in structures with braced core (less than 10%). Outrigger did not consistently reduce maximum drift under all records, except for the story where it is located. Although outrigger could not reliably decrease residual drift of structures with braced core, it significantly decreased this index when applied at any level of buildings with RC shear wall core, under all studied records. Applying outrigger increased story shears and NLTHA showed that it creates a sudden jump in shear at its placement story.

The seismic response of structural outrigger systems in the tall buildings

One of the advanced structural systems that have been applied in tall buildings to improve the building strength during quake loads is the outrigger system. Most of the previous researches interested to study the behavior of steel outrigger truss system, although the hard connection between the concrete and steel members may give us the inaccurate output. For that, This research aims to find the best structural concrete outrigger system by performing a comparison between two structural outrigger systems, the wall beam outrigger system, and the vierendeel outrigger system which makes the building facing strong actual earthquakes. All the models were analyzed in the advanced Midas-Gen software program and the building response was studied under El-Centro time history earthquake load. And also, finding the best outrigger position through the building height when the outrigger is applied in one and two stories. This comparison is built on different parameters as storey drift, storey drift ratio, and the base storey overturning moment. The results showed that a one-storey wall beam structural system is better than two stories vierendeel structural system when these systems are applied as an outrigger system. The best position for one storey outrigger is about 0.45 of the total building height and for the two stories outrigger, the 0.20 and 0.45 of the total building height are the best positions. Overall, the concrete outrigger systems are an effective structural system to make the tall buildings facing the earthquake loads.

Effects of Outrigger & Belt Truss System on High-Rise Building Structure Performance

Using the lateral stiffener system, outrigger & belt truss is one of alternative to reduce the period of fundamental vibrate, displacement, and inter-story drift on high-rise building due to earthquake. The method that used to analysis structure performance, either it used an outrigger & belt truss system or not in post-elastic seismic load condition is nonlinear static analysis with pushover. The result of pushover analysis which shown the performance of building structure when an earthquake occurs, known as performnace based design. This research use 4 models building (A-B- C-D) with 62 floors of tower and 6 floors of podium, has dual system portal combination with particular concrete shear-wall and located in the City of Jakarta which soft soil categorize. Building A doesn’t has outrigger & belt truss, meanwhile building B has it and the material of both buildings are reinforcement concrete structure. Building C doesn’t has outrigger & belt truss, meanwhile building D has it and the material of both buildings are profile steel structure. Seismic load design based on Source Map and Indonesian Earthquake Danger 2017 in analysis was determine as seismic repeat load which has possibility to become bigger during age of building structure (50 years), 2 %. Building A and B has Immediately Occupancy performance level, building C is Damage Control and building D has Immediately Occupancy performance.

Optimum design method for simplified model of outrigger and ladder systems in tall buildings using genetic algorithm

This paper presents a simplified modeling and optimization method (SMOM) to find the optimum preliminary design for tall buildings with outrigger and ladder systems. The simplification method depends on the super-elements and the dominant-degrees-of-freedom techniques to model the structure, where a new type of finite element is defined by grouping and processing a set of finite elements. For optimizing the preliminary design, a genetic algorithm was adopted to guide the updating of design variables, which were represented by the volume of the structure members, and so to minimize the cost of the structure by considering critical design constraints, such as top drift and constructability. Furthermore, results from the SMOM were compared with those from detailed finite element models in terms of the linear and nonlinear response to the lateral loads. Besides, to check the efficiency of the optimization algorithm, five study cases were considered by altering the optimized design variables in each case. These methods were developed and implemented in a MATLAB codification. It was found that the simplification method has good accuracy in predicting the lateral displacement, the fundamental period, and the core stress, but the accuracy of the stress prediction for the mega-columns, outrigger trusses, and belt-trusses was insufficient. Additionally, it was clear from the five study cases that the proposed genetic algorithm contributed to reducing the total cost by 34.6% as a maximum reduction, and it decreased the calculation time as well. Thus, the critical parameters which control the behavior of both outrigger and ladder systems were also deeply understood.

Effectiveness of outrigger and belt truss systems on the seismic behavior of high-rise buildings

Effectiveness of outrigger and belt truss systems on the seismic behavior of high-rise buildings

Seismic assessment of thin steel plate shear walls with outrigger system

The seismic performance and failure modes of the dual system of moment resisting frames and thin steel plate shear walls (TSPSWs) without and with one or two outrigger trusses are studied in this paper. These structural systems were utilized to resist vertical and lateral loads of 40-storey buildings. Detailed Finite element models associated with nonlinear time history analyses were used to examine seismic capacity and plastic mechanism of the buildings. The analyses were performed under increased levels of earthquake intensities. The models with one and two outriggers showed good performance during the maximum considered earthquake (MCE), while the stress of TSPSWs in the model without outrigger reached its ultimate value under this earthquake. The best seismic capacity was in favour of the model with two outriggers, where it is found that increasing the number of outriggers not only gives more reduction in lateral displacement but also reduces stress concentration on thin steel plate shear walls at outrigger floors, which caused the early failure of TSPSWs in model with one outrigger.