Compression Brace Research Articles

Диференційний підхід до хірургічної корекції вродженої лійкоподібної деформації грудної клітки в дітей

Pectus excavatum (PE) is the most common defect – it occurs in 0.1–0.8% of the population. This defect is characterized by changes in the cardiorespiratory system, induction of concomitant spinal deformities, severe psychological problems. Nuss surgery and most of its modifications doesn’t provide good results in the treatment of atypical anatomical variants of deformity; it is characterized by displacement and eruption of plates, chronic postoperative pain syndrome, deformity of the ribs, which encourages the search for ways to solve these problems. Purpose – to improve treatment results in patients with various forms of PE by introducing their own differentiated options for Nuss surgery and choosing the optimal size of fixation plates; to analyze the results of treatment. Materials and methods. H. J. Park classification has been used. Variants of Nuss surgery have been developed for the following types of IIA1; IIA2; IIA3; IIB, IIC. All surgeries begin with a free extension of the anterior chest wall to the physiological position with ligatures imposed on the sternum’s lower third and ribs. Horizontal plate fixation has been used in IIA1, IIA2, IIA3 types, and in IIB and II C types – its oblique fixation with a lower location of the end of the plate on depressed side. In both versions plate stabilizers are rigidly fixed to 2 (sometimes 3) ribs on both sides under the bones, and in IIB and II C types the plate stabilizer is fixed ventrally at the depressed side and dorsally at the bulging side. For surgical treatment of wide and widened deformation types we use two plates (IB, IIA2, IIA3); one plate is used for treatment of IA, IIA1, IIB, IIC deformations. In the case of the common version of the IIC – two plates. When installing two plates, the shorter upper plate is installed according to Pilegaard at IB, IIA2; standard length – with IIA3 and common version of IIC. We’ve done a mathematical modeling of the correcting plate functioning as a monolithic arched structure with rigidly fixed ends with the determination of the optimal plate width at a thickness of 2.2 mm. Also we’ve analyzed surgical treatment of 55 patients with PE operated in 2018–2020 (ІА – 25; ІВ – 6; ІІА1 – 7; ІІА2 – 3; ІІА3 – 2; ІІВ – 6; ІІС – 4). Results. Excellent and good cosmetic and functional results were revealed. Postoperative complications – 4 (7.3%). Two postoperative local asymmetric keel-like deformations were noted: one for each in treatment of IIB and IIC (successful treatment is carried out in an individual dynamic compression brace system). In one case, simple pneumothorax was diagnosed, and in another – eruption of one of the two corrective plates. Practical recommendations for determining the optimal plate width at its length of 280 mm and less – 12 mm; 290–300 mm – 13 mm; 310–320 mm – 14 mm; 330–340 mm – 15 mm; 350–360 mm – 16 mm. One month after the operation, 26 patients were surveyed according to the NRSP scale and the following results were obtained: among the operated patients with II degree of deformity: 1 point – 50.0% of patients, 2 points – 25% of patients, 0 points – 25.0% of patients (mean score – 1.0); among patients with III degree of deformity 1 point – 25% of patients; 2 points – 50%, patients 3 points – 12.5% of patients; 0 points – 12.5%, average score – 1.63. There was no chronic postoperative pain. Conclusions. Key to proposed differential approach in the PE treatment is careful planning of the operation (correct selection of the number of plates, their size, method of installation and fixation depending on the PE anatomical variant). This allows to achieve good and excellent cosmetic and functional results; minimize the number of postoperative complications. The research was carried out in accordance with the principles of the Helsinki declaration. The study protocol was approved by the Local ethics committee of all participating institutions. The informed consent of the patient was obtained for conducting the studies. No conflict of interest was declared by the authors. Key words: Nuss surgery modifications, atypical forms of pectus excavatum.

Seismic performance of steel chevron braced frames designed according to Japanese practice

Six steel braced-frame specimens and nine isolated brace specimens were tested to examine the seismic behavior of steel chevron braced frames designed and constructed according to the current Japanese practice. The braced-frame specimens placed a pair of braces in a “chevron” arrangement, in a single-bay, single-story moment-resisting frame. The braces had either a round-HSS or I section. The bracing connections adopted either slip-critical bolted connections as is the norm in Japan or a field-welded connection following U.S. recommendations. The specimens were subjected to a cyclic loading sequence that is similar in severity to the protocol specified for steel moment-resisting frames in the U.S. seismic provisions. The test results suggest that chevron braced frames with compact braces and using moment-resisting beam-to-column connections can safely develop large story drifts exceeding 0.03 rad. The force unbalance between the tension and compression braces led to large beam deflection and, in some cases, torsion, which in turn limited the tensile axial forces in the braces. The lateral resistance at key limit states matched the strength computed based on plastic analysis.

An Alternative Approach for the Design of Chevron-Braced Frames

The design of steel chevron-braced frames as per Eurocode 8 is based on the idea that only the braces should buckle and yield during ground motions, while other members should remain elastic. The elastic design of the braced frames is also allowed. However, in both cases, the seismic performance of the frame may be compromised because of premature yielding/buckling of columns. This paper proposes an alternative design procedure that promotes yielding of beams in addition to yielding of braces. This mitigates the vertical unbalanced force transmitted by compressive and tensile braces to the beam and in turn reduces the internal forces of the columns. The result is the overall improvement of the seismic performance owing to the reduction of the number of cases in which failure of the columns occurs before full exploitation of the ductility capacity of the dissipative members. The proposed design procedure is validated by incremental dynamic analyses performed on a set of chevron-braced frames. In particular, the peak ground accelerations of the frames designed by the proposed procedure at the attainment of Significant Damage and Collapse Prevention limit states are determined and compared to those of frames designed according to Eurocode 8. Furthermore, frames designed according to the Eurocodes and to the proposed method are compared in terms of structural cost.

Effects of Steel Braces on Robustness of Steel Frames against Progressive Collapse

External installation of steel braces is an effective approach to increase the lateral load resistance of steel moment-resisting frames. However, the effects of existence of steel braces on the robustness of steel moment-resisting frames to resist progressive collapse is still not clear because little study has been carried out. To fill this gap, in this paper, six multistory steel moment-resisting subframes (three bare frames and three braced frames) were fabricated and tested. Test results indicated that the specimen with reduced beam section in the connection zone performed best among three types of connections due to the guaranteed formation of plastic hinges at the location of reduced section and avoiding brittle fracture of weld at the connection. Experimental results proved that steel braces could increase the load-resisting capacity by 45.1% and 83.9% of the frame with weld connection and end plate connection, respectively. The gusset plate restricted the rotation of the plastic hinges in the second story of the braced frames with V-shaped bracing, which decreased its deformation capacity and degraded its catenary action capacity. Actually, the ultimate load of the braced frames with V-shaped bracing is only 87.5% of that of the counterpart without any braces. Because the compressive braces were severely buckled before the displacement reached 0.4% of the beam span, it had little effect on yield load but increased the initial stiffness of the bare frames. Thus, a majority of the benefits of the bracing system were attributed to the tensile braces. Moreover, the analytical results evaluated the differences in load resistance and development of load-resisting mechanisms in different stories. Furthermore, the contribution of compressive and tensile braces was decomposed individually by analytical analysis.

Modification of Buckling Restrained Braces and Evaluating the Deflection Amplification Factor

Buckling is a main problem in every structure. It is a sudden change in shape or deformation of a structural component under load. Under moderate to severe earthquakes, buckling of compressive braces may cause damage to the joints and connections. So Buckling-Restrained Braces (BRBs) have been widely implemented in framed structures to reduce damage during severe earthquakes. Unlike conventional braces that buckle under compression, the core of BRBs yields both in tension and compression under the restraining effect of the casing. A typical buckling-restrained brace (BRB) is composed of a ductile steel core, which is designed to yield in both tension and compression. To avoid global buckling in compression, the steel core is usually wrapped with a steel casing, which is subsequently filled with mortar or concrete. So in this work the deflection amplification factor of these braces are found out. As DAF predicts the maximum capacity of the structure, so a deep study in this field is necessary. DAF is the ratio of in-elastic deformations to elastic deformation. So after finding the DAF of these BRBs and by knowing the elastic deformation of the structure we can easily find the in-elastic deformation. For this works the analysis are carried out using etabs and abaqus software.

A seismic design method for one-piece gusset plate connections

In multi-story Special Concentrically Braced Frames (SCBFs), there are bracing nodes where two braces associated with two sequential adjacent stories of a similar bay intersect each other at beam-to-column joints. In these bracing nodes, under loading, one of the braces is in tension and the other is in compression. Consequently, maximum vertical force is imposed on the column. Note that in these bracing nodes, force distribution at a gusset plate affects the force distribution at the other gusset plate. Generally, two separate gusset plates are considered for the bracing nodes with two braces at the beam-to-column joints and designed according to Uniform Force Method (UFM). While the UFM proposed for corner gusset plates with one brace does not consider the force distribution effects at both gusset plates. To resolve this problem, the current study proposes a one-piece gusset plate for the bracing nodes with two braces at the beam-to-column joints. The one-piece gusset plate involves the gusset plate of the tension brace, the gusset plate of the compression brace, a part of the beam web whose length is equal to the interface of the gusset plate to the beam, and finger stiffeners. The finger stiffeners are considered in the connection region on both sides of the one-piece gusset plate to simulate the presence of the beam flanges removed in this region. Note that in this connection, the beam is extended to near the one-piece gusset plate and thereafter is connected to it. The aims of this study are as follows: (1) considering the force distribution effects on both gusset plates, (2) calculating the force and bending moment demands of the gusset plates in the bracing nodes with two braces at the beam-to-column joints via proposing a new method, and (3) determining the gusset plate dimensions in the bracing nodes with two braces at the beam-to-column joints through presenting a new procedure. Five one-bay, two-story SCBFs with the brace angles of 37−37, 45−45, 59−59, 37−59 and 59−37° (the first number is the lower story brace angle and the second number is the upper story brace angle) were designed in accordance with the method and procedure proposed in this study. These specimens were simulated in ABAQUS and subjected to a monotonic loading. The accuracy of the proposed method was confirmed via comparing the results of ABAQUS and UFM with those of the proposed method.

Mechanical behaviour of welded high strength steel rectangular hollow section joints

The material reduction factor of rectangular hollow section (RHS) joints in a new version of Eurocode 3 part 1–8 is validate for steel with the nominal yield strength up to 700 MPa. In this paper, finite element simulations of gap K-joints are conducted to investigate effects of material properties, gap size of the joint, the brace to chord width ratio and welds type on the secondary bending stresses and the resistance. The governing failure mode considered for all the FE models is the chord face failure followed by brace sidewall failure. The ratio of axial stresses to the nominal stress was lower in the compressive brace made of higher strength steel grades compared to the mild strength grades. The maximum secondary bending stresses is 0.12–0.32 yield strength. The secondary bending stresses are increasing with the increase of the steel grade and the brace to chord width ratio and with reducing the gap size. The level of secondary bending stresses varied between 38% and 56% of the average normal axial stress. The secondary bending stresses of fillet-welded joints are larger than the butt-welded joints. The yield line model is used to predict the ultimate load and good agreement is obtained compared with FE results.

Comparative Study of Open Frame Structure Modeling with Diagonal Bracing at the Integrated Laboratory of Institut Teknologi Kalimantan

Generally, brick wall (hebel) is considered as non-structural element, which never be counted to bear structural load. But, if carefully calculated, brick walls take part in structure load bearing. In the purpose of reducing the main structural element properties, the brick wall needs to be considered in bearing structural load. In this article, the brick walls modelled as compressive bracings. Using the structure analysis program, the model showed some significant differences in terms of internal force. From the analysis, the differences of moment, shear, axial and torsional force between open frame model (usual model, OF) and compressive bracing (CB) model were 38.17 kN.m; 58.03 kN; 181.75 kN dan 44.18 kN.m, respectively, where the first model had the bigger numbers than the latter model. Displacement of OF model was quite larger than CB model, with the value of difference was up to 85.35% for the X direction structures, and 70.83% for the Y direction. Final properties used for the design are smaller compared than original design, 30/60 to 40/60 for the beams, 50/50 for the columns with the different reinforcements 16-D22 for the second model compared to 20-D22 for the first one. The depth of slab on the second model was 180 mm, slightly smaller than the first model, 190 mm. It can be concluded that using compressive bracing model, structural properties of ITK Integrated Laboratory Building may greatly be reduced, compared to OF model.

Earthquake response control of ground soft storey

In the present study, friction damper, an energy dissipating passive device is explored to reduce the response of open ground storey building under lateral loading due to earthquake. This damper is installed in the selected bays of open ground storey so that the response is reduced. The masonry infill wall is macro-modeled in the form of compression only diagonal members. Three different types of bracing system were installed along with Pall friction damper – single diagonal tension – compression brace with friction damper, tension only cross brace with friction damper and chevron brace with friction damper were modeled using Wen’s plastic link element in SAP2000. G+4 storey buildings were analyzed using nonlinear time history analysis. The storey displacement and inter-storey drift for all the cases were compared in the study.

Earthquake response control of ground soft storey

In the present study, friction damper, an energy dissipating passive device is explored to reduce the response of open ground storey building under lateral loading due to earthquake. This damper is installed in the selected bays of open ground storey so that the response is reduced. The masonry infill wall is macro-modeled in the form of compression only diagonal members. Three different types of bracing system were installed along with Pall friction damper – single diagonal tension – compression brace with friction damper, tension only cross brace with friction damper and chevron brace with friction damper were modeled using Wen’s plastic link element in SAP2000. G+4 storey buildings were analyzed using nonlinear time history analysis. The storey displacement and inter-storey drift for all the cases were compared in the study.

Study on Partial Replacement of Natural Aggregate Concrete (NAC) With Recycled Aggregate Concrete (RAC)

This paper is about the use of the recycled aggregate concrete(RAC) instead of using the normal conventional concrete to reduce the usage of naturally available aggregate and it’s an alternate to preserve our natural resources, utilize the construction and demolition waste(C&D). The upgradation of living life needs a replacement and new design to remove or rehabilitate the old buildings. Will lead to tones of C& D wastes; there is limited place to dispose it. Main reason is to tackle the problems based on the waste management that has become one of the tremendous problems that cannot be resolved. The squanders that can be reused once on the off chance that it is utilized is generally best in this colossal populace society don’t have the foggiest idea where to dump every one of these squanders. Instead of disposal, our government along with researchers started utilizing this waste again in the construction in the form of Recycle aggregates like fine particle and Recycle concrete aggregate. Most of the states in India having plants in disposal area to recycle this C&D waste. From the studies it says that recycle aggregate concrete can be used for M25, M30, M35, M40 and also use in Self compacting concrete. In this paper we did experimental studies on Recycle aggregate concrete (M25) near area has been used and identify its basic properties. The cement is supplanted with reused coarse total (RCA) of two unique proportions (40, 60& 80) and their compressive quality and brace rigidity of the solid are tried. The outcomes show that the RCA of proportion 80 % has higher quality than the solid with half substitution.

An experimental study on stress concentration factors of stainless steel hybrid tubular K-joints

This paper describes a test program on the stress concentration factors (SCFs) of stainless steel hybrid tubular (SSHT) joints with square hollow section (SHS) braces and circular hollow section (CHS) chord and SSHT joints with CHS braces and SHS chord. The load was applied to the brace for all test specimens. Twenty specimens in total, including ten overlapped and ten gapped tubular K-joints, were tested. Different geometric parameters were used which include brace width-to-chord diameter ratio (β1 = b1/d0), brace-to-chord thickness ratio (τ1 = t1/t0) and chord diameter-to-thickness ratio (2γ1 = d0/t0) for SHS-to-CHS hybrid tubular joints, brace diameter-to-chord width ratio (β2 = d1/b0), brace-to-chord thickness ratio (τ2 = t1/t0) and chord width-to-thickness ratio (2γ2 = b0/t0) for CHS-to-SHS hybrid tubular joints. A number of strain gauges were used at the hot spot locations for various tubular joints. The hot spot stress (HSS) method was used to determine the SCFs of SSHT joints using the quadratic extrapolation method. This was a consequence of the stress distributions around the intersection area of SHS-to-CHS and CHS-to-SHS hybrid tubular joints being nonlinear. Results found the maximum SCFs for hybrid overlapped tubular K-joints with square braces and circular chord to be located at the hot spot location at an angle of 135° between the SHS brace and the CHS chord. This is characterized as line A. The maximum SCFs of hybrid gapped tubular K-joints with square braces and circular chord were located at the hot spot location at an angle of 45° between the SHS tension brace and the CHS chord (characterized as line C) and at an angle of 45° between the SHS compression brace and the CHS chord (characterized as line E). The maximum SCFs of hybrid overlapped tubular K-joints with circular braces and square chord were located at the hot spot location at an angle of 180° to the CHS brace. The maximum SCFs of hybrid gapped tubular K-joints with circular braces and square chord were located generally at the hot spot location at an angle of 0° to the CHS brace. Test results were compared against the design predictions in accordance with the current design guidelines of the International Committee for the Development and Study of Tubular Structures (CIDECT, 2001). Upon comparison, it was found that the design formulas of CIDECT (2001) overestimate the maximum SCFs of SHS-to-CHS hybrid gapped tubular K-joints. For the CHS chord and SHS braces of hybrid overlapped tubular K-joints, the design formulas overestimate the maximum SCFs for most of the specimens. Furthermore, for the SHS chord and CHS braces of hybrid gapped tubular K-joints, the design formulas of CIDECT (2001) overestimate the maximum SCFs. For the SHS chord and CHS braces of hybrid overlapped tubular K-joints, the CIDECT (2001) design formulas were unconservative when determining the maximum SCFs of such joints.

Usefulness of 3-Dimensional Body Surface Scanning in the Evaluation of Patients with Pectus Carinatum.

BackgroundRadiographic modalities have been commonly used to evaluate pectus carinatum (PC), and compressive orthotic bracing is the most widely accepted treatment method. The aim of this study was to determine the efficacy of 3-dimensional (3D) body surface scanning as an alternative modality for the evaluation of PC.MethodsThe medical records of 63 patients with PC who were treated with compressive orthotic bracing therapy between July 2017 and February 2019 were retrospectively analyzed. Using both 2-view chest radiography (posteroanterior and lateral view) and 3D body scanning, the height of maximal protrusion of the chest wall was measured both before and after 2 weeks of bracing therapy. The difference between the pre- and post-treatment measurements was calculated for both modalities, and these differences were compared and analyzed.ResultsBased on the comparison between the pre- and post-treatment radiographs, bracing therapy produced favorable outcomes in all patients (p<0.001). The measurements obtained via 3D scanning were strongly correlated with those obtained via chest radiography (r=0.60).ConclusionBased on the findings of this study, 3D body surface scanning appears to be an effective, radiation-free, and simple method for the post-treatment follow-up evaluation of PC, and thus can be considered an alternative to radiography.

Seismic performance of chevron‐configured special concentrically braced frames with yielding beams

SummaryCurrent seismic design requirements for special concentrically braced frames (SCBFs) in chevron configurations require that the beams supporting the braces be designed to resist the demands resulting from the simultaneous yielding of the tension brace and degraded, post‐buckling strength of the compression brace. Recent research, including large‐scale experiments and detailed finite‐element analyses, has demonstrated that limited beam yielding is not detrimental to chevron braced frame behavior and actually increases the story drift at which the braces fracture. These findings have resulted in new expressions for computing beam demands in chevron SCBFs that reduce the demand in the tension brace to be equal to the expected compressive capacity at buckling of the compression brace. In turn, the resultant force on the beam is reduced as is the required size of the beam. Further study was undertaken to investigate the seismic performance of buildings with SCBFs, including chevron SCBFs with and without yielding beams and X‐braced frames. Prototype three‐ and nine‐story braced frames were designed using all three framing systems, that is, chevron, chevron with yielding beams, and X SCBFs, resulting in six building frames. The nonlinear dynamic response was studied for ground motions simulating two different seismic hazard levels. The results were used to characterize the seismic performance in terms of the probability of salient damage states including brace fracture, beam vertical deformation, and collapse. The results demonstrate that the seismic performance of chevron SCBFs with limited beam yielding performs as well as or better than the conventionally designed chevron and X SCBFs.

Does physiotherapy applied in conjunction with compression brace treatment in patients with pectus carinatum have efficacy? A preliminary randomized-controlled study.

Non-invasive treatment of pectus carinatum (PC) deformity includes the use of a compression brace and exercises. In this study, we aimed to examine the effect of a physiotherapy protocol applied as adjunct to compression brace treatment in patients with PC. The study included 30 male patients between 11 and 18years of age. Patients were randomly assigned into two groups: a brace treatment only group (Group 1) and a brace and physiotherapy group (Group 2). Patient demographics and disease-related properties, protrusion measurements, postural evaluations, deformity perceptions, life quality, and treatment satisfaction were evaluated. Although both groups showed improvements based on external chest measurements related to PC protrusion following treatment (p < 0.001), Group 2 had more benefit from the treatment (effect size > 0.36) and displayed greater improvement in maximum protrusion degree and lateral length values (p < 0.05). Additionally, we found that patient perception of deformity, posture, psychological life quality, and treatment satisfaction scores were significantly better in Group 2 (p < 0.05). Owing to the satisfaction and additional benefits observed in the physiotherapy group, we think that a proper cardiopulmonary and musculoskeletal exercise program should be applied concurrently with brace treatment for patients with PC deformity. Nevertheless, long-term outcomes need to be clarified in future studies.

Challenges in calculation of critical buckling load of tubular members of jacket platforms in finite element modeling

Accurate estimation of the capacity curve of offshore jacket structures to achieve performance levels and ductility is of great importance. Proper modeling of compressive members to correctly investigate global and local buckling is crucial in estimation of the capacity curve. Buckling modes and deformations due to local buckling can be considered, if the compressive braces are modeled by shell or solid elements. The purpose of this paper is to achieve the correct compressive behavior of braces with solid type elements and investigate the effects of five different parameters such as D/t, L/D, mesh size, mesh size ratio, and imperfections. ABAQUS FE software is used for this purpose. The percentage of difference between model results and ISO equation for critical buckling load and the best choice of the above variables has been presented to achieve the maximum precision. Also the effect of these parameters on buckling capacity curve of tubular members has been estimated. The percentage of the effect of mentioned parameters is shown as separate pie charts. Consequently, mesh size ratio has the greatest effect on elastic stiffness and post-buckling strength. On the other side, the imperfection value is the most effective parameter on critical buckling load.

Initial reduction of flexible pectus carinatum with outpatient manipulation as an adjunct to external compressive bracing: technique and early outcomes at 12 weeks

IntroductionOur aim was to assess whether initial reduction with outpatient soft-tissue manipulation of flexible pectus carinatum deformity prior to external compressive bracing was associated with improved compliance and patient satisfaction compared to reported outcomes of external brace with progressive tightening. Materials and methodsFrom our observational cohort of 227 patients, 177 were felt appropriate to undergo initial reduction and soft tissue manipulation prior to immediate custom fitting of an external compressive brace. These patients then followed a prescriptive schedule of 12 weeks of continuous external bracing with subsequent follow-up in clinic. ResultsThe reduction in Haller Index was maintained throughout the period of external bracing without the need for progressive tightening of the external brace. The treatment was associated with high levels of patient satisfaction and high patient concordance compared to other protocols. There were no major complications and minor complications included only skin irritation. ConclusionsOut-patient initial reduction with manipulation prior to external compressive bracing is a novel technique which resulted in excellent concordance and high rates of patient satisfaction and should be considered as an adjunct to standard external bracing techniques. Type of StudyTreatment Study. Level of EvidenceLevel II.

External Compressive Bracing With Initial Reduction of Pectus Carinatum: Compliance Is the Key

To assess the impact of manipulation and a tailored program for compressive bracing on the quality of life of patients with flexible pectus carinatum. Two hundred forty-nine sequential patients attending a clinic for assessment of pectus carinatum deformities underwent outpatient manipulation and then followed a prescribed schedule of continuous external compressive bracing but without significant progressive tightening. There was successful sustained reduction of the deformity in 244 patients with high reported rates of concordance (98%) and satisfaction (94%). Patients experienced a reduction in symptoms of anxiety and depression (P < .001) and had improved body satisfaction (P < .001). Mild skin irritation occurred in 18% of patients (n= 44), and there were 2 severe cases of skin irritation, 1 of which resulted in abandonment of bracing. Manipulation and nontightening compressive bracing was associated with complete concordance, high levels of successful bracing, improved confidence, and reduced psychological morbidity.

Capacity Evaluation of Ressalat Jacket of Persian Gulf Considering Proper Finite Element Modeling of Tubular Members

The capacity curve obtained from the pushover analysis of jacket-type offshore platforms gives their structural performance levels, ultimate capacity and ductility. Accurate estimation of structural capacity curve is of great importance. Accurate modeling of the global and local buckling of compression tubular members in a correct form is an effective part of studying the behavior of offshore jackets under all various types of loading conditions at any given time of their life. Modeling of compressive braces by shell or solid elements when the imperfections are applied leads to deformations due to local buckling based on buckling modes. This paper aims to achieve more accurate compressive behavior of compression members. The ABAQUS finite element software has been used for this purpose. Regarding to the results achieved from investigation of buckling in tubular members proper elements have been introduced to investigate the global and local buckling phenomena. Then pushovers results of Ressalat jacket with conventional modeling versus more accurate modeling proposed in this paper for compressive members have been compared as a case study. According to the results applying improper mesh size for compressive members can under-predict the ductility by 33% and under-estimate the lateral loading capacity up to 8%. Finally, ISO equations and Marshall strut theory have been applied to investigate critical buckling load and post-buckling response of tubular braces. The innovation of this paper is investigating the interaction of global and local buckling in the braces of jacket with 1-Dimentional elements using ISO equations and buckling envelope derived from the solid element results, which results in low computational costs.

Dissipative connections with U-shaped steel plate for braces of concentrically braced frames

In concentrically braced frames, braces-to-adjacent member connections are suitable locations for the dissipation of seismic energy. If the implementation of dissipative connections does not compromise the global lateral stiffness of the structure, the compression braces can then be protected from buckling, while the structural ductility is increased and the action effects reduced. Furthermore, an efficient use of dissipative connections allows reducing the cost of post-earthquake interventions. In this paper, an innovative dissipative connection for braced frames is proposed, consisting of a steel plate bent to a U shape and connecting the brace to the adjacent column. In this connection, energy dissipation is obtained through the inelastic flexural deformation that takes place in the plate. This paper presents experimental results on the isolated U-connection and on single-storey concentrically braced frame (real scale) including the U-connection. Besides considering several variations on the geometry of the U-shape plate, the tests considered both monotonic and cyclic loading. The results highlight the efficiency of the U-connection to dissipate the energy input through inelastic deformations. On the other hand, the cyclic tests show however that the connection is potentially sensitive to fatigue, as the deformation capacity is significantly reduced with repeated loading and increasing stress amplitude, requiring thus specific attention in practical design situations.