Greater Structural Stiffness Research Articles

Enhancing fixation stability in proximal humerus fractures: screw orientation optimization in PHILOS plates through finite element analysis and biomechanical testing

The optimal treatment strategy for proximal humerus fractures (PHFs) is debatable owing to the relatively high failure rate of locking plates. Optimizing implants may enhance the fixation stability of PHFs and reduce the rate of mechanical failures. We developed a finite element (FE) model to simulate the treatment of PHFs with Proximal Humerus Internal Locking System (PHILOS) plates. The model evaluated the average bone strain around the screw tips under vertical loading (as an alternative to the risk of cyclic screw cutout failure verified through biomechanical testing) to minimize this strain and maximize predicted fixation stability. After determining the optimal screw configuration, further FE analysis and in vitro biomechanical testing were conducted on both standard and optimized PHILOS screw orientation to assess whether the optimized plates have biomechanical advantages over the standard plates. The FE-based optimized configuration exhibited significantly lower bone strain around the implant than the standard PHILOS screw orientation (− 17.24%, p < 0.001). In both FE analysis and in vitro biomechanical testing, the optimized PHILOS plates achieved significantly lower average bone strain around the screws (p < 0.05), more uniform stress distribution, and greater structural stiffness (p < 0.05) than the standard PHILOS screw orientation. Our results show that biomechanical performance of the PHILOS plates can be improved by altering the orientation of the locking screws. This approach may be useful for future patient-specific design optimization of implants for other fractures.

Discussion on cable-strut systems of the suspen-dome structures

According to the architectural requirements, the roof structure of a large-span gymnasium adopts the suspen-dome structure. In the scheme selection stage of the pre-stressed cable-strut system at the bottom part of the suspen-dome structure, a Levy-type scheme and a Loop-free scheme are established. The finite element models are established, and the static analysis under the design loads, the whole process analysis of load-displacement, and the dynamic response analysis after accidental cable break are carried out. The architectural expression of the two schemes are discussed. The component material consumption, the structural stiffness, the tension distribution characteristics, and the static bearing capacity of the two schemes are discussed. The failure mode and the progressive collapse resistance of the two schemes after accidental cable break are also discussed. The results show that the Loop-free scheme requires significantly less in terms of component material consumption than the Levy-type scheme. The static failure mode of the two schemes is strength failure, but the Loop-free scheme has greater bearing capacity. The Loop-free scheme has greater structural stiffness, lower cable forces, and uniformly distributed cable forces in each layer, and lower stress on the top reticulated shell members. Neither of the two schemes experience progressive collapse after accidental cable break. Due to the rupture in the loop cable of the Levy-type scheme, the rigidity of the rear region decreases greatly, and the cable force loss is large. On the contrary, internal force redistribution occurs in the Loop-free cable scheme and the cable force loss is not obvious, hence the progressive collapse resistance is better than that of the Levy-type scheme.

Long adhesive joints in façade applications exposed to wind suction

This paper provides an insight into the investigation of long thick-layer adhesive façade joint resistance to negative pressure loads, i.e. wind suction. The real structural response to wind actions was simulated with reference to ETAG 034. Each specimen represented a reference façade section. The experiment focused on four different adhesive systems with flexible high strength 1-K polyurethanes and 1-K modified silyl polymers. Several variants of the test assemblies were tested: 1) a test assembly with an adhesive joint when a) the manufacturers’ application instructions for the system were followed and b) the instructions were violated; 2) a test assembly with a mechanical joint. These variants made it possible to compare the properties of both fastening methods, and moreover, to assess the impact of the mounting tape on the properties of the adhesive joint. The comparison of adhesive joints and a mechanical joint proved the greater structural stiffness and stress resistance of bonded assemblies. Monitoring showed that a local failure of the fastening element between the load-bearing frame and supporting structure caused the failure of the bonded assemblies, whereas the specimen with mechanically attached cladding failed due to pull-through of the fasteners. The average failure load of the bonded assembly was 10.88 kPa. In contrast, the failure load of the segment with mechanical fasteners was 10.12 kPa. Even though the difference in maximum pressure loads was only around 7%, the recorded values clearly demonstrate that the weakest part of the whole façade system is the mechanical joint, not the bonded one. Furthermore, the comparison of the results for segments with and without mounting tape showed that tape can have a major impact on the bond strength, since in case of the test specimens without mounting tape, the recorded failure load was a maximum of 30% higher.

Comparative Study on the Lateral Load Resistance of Multi-Storied Structure with Bracing Systems

The vulnerability of seismic forces onto a high rise structure leads to a sudden collapse which is unpredictable. It can also be understood from the provisions of Indian Standards that, it is desired to allow the damage of the structure to certain extent for sudden earthquakes by safeguarding the livelihood. In the present study, a five storied RC building has been modeled and then analyzed considering the combination of gravity and seismic forces. The performance of the same structure has been investigated for different types of bracing system such as cross and diagonal bracings using a concrete section and steel sections respectively. The performance of the same building has been evaluated in terms of lateral displacement of members, storey drift, axial force and bending moment in columns at different critical. The effectiveness of various bracing systems on the structure has also been investigated. More importantly, the reduction in lateral displacement has been found out for different types of bracing system in comparison to building with no bracing for zone-3 and zone-4. From the present study, it has been found that the crossed ‘X’ bracing reduces more lateral displacement and thus significantly contributes to greater structural stiffness to the structure.

Numerical investigation on the wind stability of super long-span partially earth-anchored cable-stayed bridges

To explore the favorable structural system of cable-stayed bridges with ultra-kilometer main span, based on a fully self-anchored cable-stayed bridge with 1400 m main span, a partially earth-anchored cable-stayed bridge scheme with the same main span is designed. Numerical investigation on the dynamic characteristics, aerostatic and aerodynamic stability of both two bridge schemes is conducted, and the results are compared to those of a suspension bridge with similar main span, and considering from the aspect of wind stability, the feasibility of using partially earth-anchored cable-stayed bridge in super long-span bridges with ultra-kilometer main span is discussed. Moreover, the effects of structural design parameters including the length of earth-anchored girder, the number of auxiliary piers in side span, the height and width of girder, the tower height etc on the dynamic characteristics, aerostatic and aerodynamic stability of a partially earth-anchored cable-stayed bridge are analyzed, and their reasonable values are proposed. The results show that as compared to fully self-anchored cable-stayed bridge and suspension bridge with similar main span, the partially earth-anchored cable-stayed bridge has greater structural stiffness and better aerostatic and aerodynamic stability, and consequently becomes a favorable structural system for super long-span bridges with ultra-kilometer main span. The partially earth-anchored cable-stayed bridge can achieve greater stiffness and better wind stability under the cases of increasing the earth-anchored girder length, increasing the height and width of girder, setting several auxiliary piers in side span and increasing the tower height.

Design Analysis of a Machined Part in a Single Step to Replace a Structural Component Assembled through Non-destructive Testing and FEA

In this study, a design analysis was performed through non-destructive test by rectangular rosette and uniaxial strain gages with FEA, between a structural aerospace assembled component of aluminium and a proposal part machined in one step with the same geometric characteristics. The analysis showed that the proposal part machined in one step has a trend to obtain less strain (0.5156mɛ@46.44N rectangular rosette strain gage, 0.4796 FEA) than the assembled component (0.7012mɛ@46.44N rectangular rosette strain gage, 0.7793 FEA). These findings indicate that the proposal part is a structural element with greater structural stiffness in comparison to the assembled component.

Investigation on mechanics performance of cable-stayed-suspension hybrid bridges

The cable-stayed-suspension hybrid bridge is a cooperative system of the cable-stayed bridge and suspension bridge, and takes some advantages and also makes up some deficiencies of both the two bridge systems, and therefore becomes strong in spanning. By taking the cable-stayed-suspension hybrid bridge, suspension bridge and cable-stayed bridge with main span of 1400 m as examples, the mechanics performance including the static and dynamic characteristics, the aerostatic and aerodynamic stability etc is investigated by 3D nonlinear analysis. The results show that as compared to the suspension bridge and cable-stayed bridge, the cable-stayed-suspension hybrid bridge has greater structural stiffness, less internal forces and better wind stability, and is favorable to be used in super long-span bridges.

A new internal fixation concept for the distal femoral fracture after total knee arthroplasty

A new internal fixation concept for the supracondylar femoral fracture after total knee arthroplasty (TKA) was investigated. In the new design, the intramedullary nail was fixed on the modified femoral component of the total knee prosthesis by a locking screw. The new internal fixator complex should have greater structural stiffness by increasing the structure contact area between bone and implant. To test this improvement, biomechanical tests were conducted to compare the mechanical properties (axial and torsional stiffness) of the fractured femurs that were stabilized by three different fixators (DCS plate, GSH nail and new design fixator). The compressive test and torsional test were done by the MTS Bionix858 to compare the mechanical stability of these fixators. The results showed no significant difference among groups in compressive stiffness, which meant that these three fixators could stabilize the fracture effectively in the longitudinal direction. The torsional stiffness of all three fixation groups were lower than the Intact group with significant difference. But the torsional stiffness of the new designed fixator was higher than the DCS plate and the GSH nail. The results supported the new design concept's practicality. The new design also has better initial stability in the fixation of a supracondylar femoral fracture after TKA.

1995 William J. Stickel Silver Award. Structural analysis of absorbable pin and screw fixation in first metatarsal osteotomies.

The structural characteristics of 4.0-mm stainless steel screws compared with 4.0-mm poly-L-lactic acid absorbable screws and 2.0-mm stainless steel Steinmann pins compared with 2.0-mm poly-L-lactic acid absorbable pins in oblique closing base wedge osteotomies of the first metatarsal were evaluated. The authors performed oblique closing base wedge using an osteotomy guide in six matched pairs of fresh frozen first metatarsal bones. Fixation was achieved with either a 4.0-mm stainless steel screw or poly-L-lactic acid absorbable screw. An additional five pairs of matched specimens were used to compare 2.0-mm stainless steel and poly-L-lactic acid absorbable pins with the same approach. Specimens were loaded to failure with the Bionix Material Testing System at a constant rate of 0.166 mm/sec. A Student's t-test for paired samples was used with a 95% confidence interval to measure differences in ultimate load, ultimate displacement, and structural stiffness. There was not a significant difference in any of the parameters evaluated in the 4.0-mm poly-L-lactic acid absorbable versus stainless steel screw comparison (P > 0.05). Stainless steel 2.0-mm pins had significantly greater structural stiffness (P = 0.032) and less ultimate displacement (P = 0.021) than their poly-L-lactic acid absorbable counterparts. There was not a significant difference in ultimate load in poly-L-lactic acid absorbable and stainless steel pins (P = 0.59).

Comparison of allograft/endoprosthetic composites with a step‐cut or transverse osteotomy configuration

This study was designed to compare the biomechanical and functional characteristics of allograft/endoprosthetic composites of the proximal 25% of the femur repaired with either a transverse or a step-cut osteotomy, using a canine model (10 dogs, five with each type of osteotomy). Serial radiography and weight-bearing studies were performed monthly, and mechanical testing was done 6 months after surgery. The femora were tested in torsion and compared with the contralateral control (insertion of a femoral component but no osteotomy). At 6 months, the composites with a step-cut osteotomy had 36% greater structural stiffness than the composites with a transverse osteotomy (p < 0.005) and 121% greater maximum torque at failure than the controls (p < 0.005), without greater structural stiffness. Evaluation of peak vertical ground reaction forces revealed significantly greater weight-bearing on the experimental limb in dogs with a transverse osteotomy. The results of this relatively short-term study were mixed. Despite the increased structural stiffness of the allograft/endoprosthetic composite with a step-cut osteotomy, the dogs with this type of reconstruction had decreased weight-bearing throughout the course of the study. The step-cut osteotomy may augment the stability of the allograft/endoprosthetic composite, allowing faster healing (as demonstrated by the results of mechanical testing), but in some way, not understood, may cause pain in the reconstructed limb. Longer term studies are needed to answer these questions and to determine whether alteration of the traditional transverse osteotomy has any advantage.