Collapse Pattern Research Articles

The predictive value of drug-induced sleep endoscopy for CPAP titration in OSA patients.

The aim of this study was to identify possible upper airway obstructions causing a higher continuous positive airway pressure (CPAP) titration level, utilizing drug-induced sleep endoscopy (DISE). A total of 76 patients with obstructive sleep apnea (OSA) underwent CPAP titration and DISE. DISE findings were recorded using the VOTE classification system. Polysomnographic (PSG) data, anthropometric variables, and patterns of airway collapse during DISE were analyzed with CPAP titration levels. A significant association was found between the CPAP titration level and BMI, oxygen desaturation index (ODI), apnea-hypopnea index (AHI), and neck circumference (NC) (P < 0.001, P < 0.001, P < 0.001, and P < 0.001, respectively, by Spearman correlation). Patients with concentric collapse of the velum or lateral oropharyngeal collapse were associated with a significantly higher CPAP titration level (P < 0.001 and P = 0.043, respectively, by nonparametric Mann-Whitney U test; P < 0.001 and P = 0.004, respectively, by Spearman correlation). No significant association was found between the CPAP titration level and any other collapse at the tongue base or epiglottis. By analyzing PSG data, anthropometric variables, and DISE results with CPAP titration levels, we can better understand possible mechanisms resulting in a higher CPAP titration level. We believe that the role of DISE can be expanded as a tool to identify the possible anatomical structures that may be corrected by oral appliance therapy or surgical intervention to improve CPAP compliance.

Aerodynamic profiling of terminal building using computational fluid dynamics approach

A case study of isolated building is studied using ANSYS CFX and SAP2000. The plan idea of 30m by 60m is chosen for terminal building. The model is subjected to different wind incidence from 0° to 90° and 45° with 30° interval for 55m/s wind speed. By using tributary area method, the forces at the each mesh node are summed up to get corresponding wind force at that joint within that area. The best effective structural system is determined by designing the structure for each wind incidence. Wind analysis and design is carried out for increasing wind speed above 55m/s to identify the collapse pattern of structure. External supporting members are suggested to withstand that maximum wind speed.

Does Sleep Endoscopy Staging Pattern Correlate With Outcome of Advanced Palatopharyngoplasty for Moderate to Severe Obstructive Sleep Apnea?

Although drug-induced sleep endoscopy (DISE) is an accepted method to localize upper airway obstruction, it is not known whether all sites identified by DISE must be treated to achieve sufficient apnea-hypopnea index (AHI) improvement. The aim of this study was to compare outcomes for unilevel (upper) versus multilevel DISE collapse patterns in a patient cohort that only underwent modern palatopharyngoplasty. Our hypothesis was that not all tongue base-level obstructions on DISE must be treated. Thirty-eight patients with mean AHI of 45 events/h underwent DISE followed by palatopharyngoplasty. Outcome was measured by polysomnography or home sleep apnea testing. Eleven patients (29%) had multilevel, complete tongue base obstruction and nineteen (50%) had no obstruction. These two groups were similar in age, body mass index, and AHI; the complete group had smaller tonsils and higher tongue position. The postoperative success rate and AHI in the group without tongue base obstruction were not significantly different from those of the complete group (68%; 17.4 ± 11.0 versus 73%; 15.4 ± 20.5, P > .99). Seventeen patients (45%) had circumferential collapse of velum. The postoperative AHI was higher for patients with circumferential collapse (23.6 ± 15.8 from 55.3 ± 22.1 versus 10.5 ± 9.94 from 36.4 ± 16.7, P < .0001), but both groups had clinically and statistically significant AHI reductions. Patients with multilevel obstruction on DISE, treated with palatopharyngoplasty alone, had similar AHI outcome as those with unilevel obstruction. Multilevel surgery may not be needed in some patients with a multilevel obstruction pattern. Circumferential collapse of velum, however, was associated with a higher residual AHI.

Damage quantification, damage limit state criteria and vulnerability analysis for single-layer reticulated shell

In this paper, a ductile damage constitutive model was used to describe the damage evolution of material while a structure is subjected to earthquake loading. And embedding this constitutive model into UMAT subroutine using software ABAQUS to introduce damage constitutive equations. A damage index which includes both maximum and cumulative deformations was then used to estimate the different degrees of damage of structural members caused by cyclic loading. The collapse mechanism of single-layer reticulated shell was investigated through incremental dynamic analysis (IDA). Two types of collapse, dynamic instability and dynamic strength failure, were obtained. It was found that material damage accumulation had little effect on plastic development and collapse pattern when the structure was in dynamic instability; but the effect of material damage accumulation was obvious and could not be ignored when the structure was in dynamic strength failure due to large plastic development. Last, two different structural damage models—one including multiple structural responses and the other including deformation and energy—are defined based on limit state criteria. It was found through comparison of results that these two structural damage models can be used to accurately define and quantify different damage degrees of single-layer reticulated shells during earthquake. The vulnerability at different damage degrees of structure using the structural damage model was conducted through IDA analysis, which could be used for seismic performance evaluation and risk assessment.

Computed Tomography Characterization and Comparison With Polysomnography for Obstructive Sleep Apnea Evaluation

We hypothesized that computed tomography (CT) combined with portable polysomnography (PSG) might better visualize anatomic data related to obstructive sleep apnea (OSA). The present study evaluated the CT findings during OSA and assessed their associations with the PSG data and patient characteristics. We designed a prospective cross-sectional study of patients with OSA. The patients underwent scanning during the awake state and apneic episodes. Associations of the predictor variables (ie, PSG data, respiratory disturbance index [RDI]), patient characteristics (body mass index [BMI], neck circumference [NC], and waist circumference [WC]), and outcome variables (ie, CT findings during apneic episodes) were assessed using logistic regression analysis. The CT findings during apneic episodes were categorized regarding the level of obstruction, single level (retropalatal [RP] or retroglossal [RG]) or multilevel (mixed RP and RG), degree of obstruction (partial or complete), and pattern of collapse (complete concentric collapse [CCC] or other patterns). A total of 58 adult patients with OSA were scanned. The mean±standard deviation for the RDI, BMI, NC, and WC were 41.6±28.55, 27.80±5.43kg/m2, 38.3±4.3cm, and 93.8±13.6cm, respectively. No variables distinguished between the presence of single- and multilevel airway obstruction in the present study. A high RDI (≥30) was associated with the presence of complete obstruction and CCC (odds ratio 6.33, 95% confidence interval 1.55 to 25.90; and odds ratio 3.77, 95% confidence interval 1.02 to 13.91, respectively) compared with those with a lesser RDI. An increased RDI appears to be an important variable for predicting the presence of complete obstruction and CCC during OSA. Scanning during apneic episodes, using low-dose volumetric CT combined with portable PSG provided better anatomic and pathologic findings of OSA than did scans performed during the awake state.

Fibronasolaringoscopia en el diagnóstico de síndrome de apnea-hipopnea obstructiva del sueño (SAHOS)

En los pacientes con diagnóstico de trastornos respiratorios del sueño (TRS) no se ha podido asociar ningún hallazgo anatómico a la severidad de la patología que el paciente presenta o a su éxito quirúrgico. Los avances actuales en la tecnología de video han permitido evaluar de manera más fidedigna las medidas de la vía aérea (VA) y trazar un mapa más exacto del sitio específico de obstrucción. La fibronasolaringoscopia es una técnica accesible y económica para la evaluación de la VA en múltiples posiciones en períodos de sueño y vigilia; esta requiere un amplio conocimiento por parte del examinador de la anatomía y fisiología de la vía aérea superior para determinar los sitios exactos de obstrucción y los patrones de colapso que podrían determinar la posibilidad del manejo quirúrgico o no, haciendo de este examen diagnóstico parte fundamental en el estudio de los pacientes con TRS.

Incremental dynamic analysis of seismic collapse of super‐tall building structures

SummaryIn the present work, the incremental dynamic analysis is performed for the super‐tall building structure of ZhongNan Center, which is more than 700 m high and is currently under construction in Suzhou, China. The Chi‐Chi earthquake record is used as the ground motion input. The peak ground accelerations are scaled to five levels including 0.2 g, 0.4 g, 0.8 g, 1.4 g, and 2.0 g. The plastic damage model is adopted to represent the material failure. The finite element model is developed by using fiber beam elements for beam‐columns and laminated shell elements for shear walls and slabs. Under the attack of strong seismic ground motions, the super tall structure experiences overall collapse, which is well captured by the developed finite element model. More importantly, the collapse patterns of the super tall structure are rather different under the excitations of earthquake records with same wave pattern but different peak accelerations.

Effect of horizontal rectus surgery for the correction of intermittent exotropia on sub-A or sub-V pattern.

We evaluated effect of horizontal rectus surgery on sub-A or sub-V pattern intermittent exotropia. We enrolled patients with sub-A or sub-V pattern intermittent exotropia. The sub-A pattern was diagnosed when the eyes diverged less than 10 prism diopters (PD) from upgaze to downgaze, and sub-V pattern when the divergence was 14 PD or less from downgaze to upgaze. Patients had undergone horizontal rectus surgery without vertical transposition of horizontal rectus muscle or oblique muscle weakening. The patients were divided into two groups: sub-A pattern (group A) and sub-V pattern (group V). The outcome measures were change of amount of pattern and rate of collapse of pattern postoperatively. The amount of pattern (vertical incomitance) was amount of difference in exodeviation between upgaze and downgaze. Collapse of pattern was defined as disappearance of difference in exodeviation between upgaze and downgaze. In groups A and V, preoperative amounts of pattern were 4.9 PD and 6.8 PD, respectively. A significant reduction in amount of pattern was observed in both groups throughout the follow-up period (p<0.05). At postoperative 6 months, the amounts of pattern were 1.0 PD and 1.2 PD and the extents of reduction in amount of pattern were 4.4 PD and 5.9 PD. The rates of collapse of pattern at postoperative 6 months were 77.8 and 60.0%, respectively. In the patients with sub-A or sub-V pattern exotropia, horizontal rectus surgery without vertical transposition or oblique muscle weakening can successfully collapse the pattern.

Rapid, Quantitative Assessment of Submerged Cultural Resource Degradation Using Repeat Video Surveys and Structure from Motion

Monitoring, managing and preserving submerged cultural resources (SCR) such as shipwrecks can involve time consuming detailed physical surveys, expensive side-scan sonar surveys, the study of photomosaics and even photogrammetric analysis. In some cases, surveys of SCR have produced 3D models, though these models have not typically been used to document patterns of site degradation over time. In this study, we report a novel approach for quantifying degradation and changes to SCR that relies on diver-acquired video surveys, generation of 3D models from data acquired at different points in time using structure from motion, and differencing of these models. We focus our study on the shipwreck S.S. Wisconsin, which is located roughly 10.2 km southeast of Kenosha, Wisconsin, in Lake Michigan. We created two digital elevation models of the shipwreck using surveys performed during the summers of 2006 and 2015 and differenced these models to map spatial changes within the wreck. Using orthomosaics and difference map data, we identified a change in degradation patterns. Degradation was anecdotally believed to be caused by inward collapse, but maps indicated a pattern of outward collapse of the hull structure, which has resulted in large scale shifting of material in the central upper deck. In addition, comparison of the orthomosaics with the difference map clearly shows movement of objects, degradation of smaller pieces and in some locations, an increase in colonization of mussels.

Step-wise drops in modularity and the fragmentation of exploited marine metapopulations

Many nearshore species are distributed in habitat patches connected only through larval dispersal. Genetic research has shown some spatial structure of such metapopulations and modeling studies have shed light onto possible patterns of connectivity and barriers. However, little is known about human impact on their spatial structure and patterns of connectivity. We examine the effects of fishing on the spatial and temporal dynamics of metapopulations of sedentary marine species (red sea urchin and red abalone) interconnected by larval dispersal. We constructed a metapopulation model to simulate abalone and sea urchin metapopulations experiencing increasing levels of fishing mortality. We performed the modularity analysis on the yearly larval connectivity matrices produced by these simulations, and analyzed the changes of modularity and the formation of modules over time as indicators of spatial structure. The analysis revealed a strong modular spatial structure for abalone and a weak spatial signature for sea urchin. In abalone, under exploitation, modularity takes step-wise drops on the path to extinction, and modules breakdown into smaller fragments followed by module and later metapopulation collapse. In contrast, sea urchin showed high modularity variation, indicating high- and low-mixing years, but an abrupt collapse of the metapopulation under strong exploitation. The results identify a disruption in larval connectivity and a pattern of collapse in highly modular nearshore metapopulations. These results highlight the ability of modularity to detect spatial structure in marine metapopulations, which varies among species, and to show early changes in the spatial structure of exploited metapopulations.

0561 UPPER AIRWAY STIMULATION FOR OBSTRUCTIVE SLEEP APNEA: COMBINED NORTHEAST OUTCOMES

Obstructive sleep apnea (OSA) is associated with cardiopulmonary disorders such as hypertension, cardiac arrhythmias, and heart failure. Continuous positive airway pressure, oral appliances, and surgeries to alter upper airway anatomy, are currently in use to treat OSA. However in some patients, these treatments are either ineffective or fail due to inadequate adherence. The hypoglossal nerve stimulation (HNS) system has been shown to reduce airway collapse and improve sleep measures. This multicenter study aims to review preoperative characteristics, somnography outcomes, quality-of-life measures, compliance, complications, and effects on cardiopulmonary morbidity in patients with HNS implantation. Patients with moderate to severe OSA who have failed traditional interventions and exhibit anterior-posterior velopharyngeal airway collapse on drug-induced sleep endoscopy (DISE) underwent HNS implantation. Demographics, cardiopulmonary comorbidities, Epworth Sleepiness Scores (ESS), and polysomnography measures were collected preoperatively. Postoperatively, device titration parameters, compliance, repeat polysomnography, tongue protrusion patterns, ESS, cardiopulmonary conditions, and complications were assessed. A nonparametric Wilcoxon signed-rank test was used to compare pre- and postoperative Apnea-Hypopnea Index (AHI). Twenty-seven patients (5 female, 22 male) from Middlesex Hospital and New York Presbyterian Hospital underwent HNS implantation between December 2014 and September 2016. Mean age was 53.4 ± 8.2 years. Mean preoperative body mass index was 28.5 ± 3.5 kg/m2. Postoperative AHI was significantly reduced (44.8 ± 16.8 to 6.3 ± 8.8, p<0.001). Of the 27 patients, 14 (51.9%) achieved cure AHI < 5. Twenty-three (85.2%) achieved an AHI < 15. Mean compliance was 50.3 ± 9.2 hours/week. There was a low rate of complications: one patient had syncope on postoperative day two, two reported persistent pain at the first postoperative visit, one patient developed a hypertrophic scar, and there was one case of mild tongue paresis, which resolved spontaneously. Preliminary data show that HNS is a safe procedure associated with improved OSA outcomes. Efforts are ongoing to examine the influence of airway collapse pattern, device titration, and tongue protrusion on device efficacy. As patients are followed for multiple years, the effect of HNS on cardiopulmonary comorbidities will be further assessed. N/A.

Analysis of the seismic collapse of a high-rise power transmission tower structure

In this paper, an explicit dynamic analysis method is proposed to calculate the progressive collapse of a high-rise power transmission tower structure subjected to earthquake; the failure rule for member elements and the effect of different ground motion inputs and tower heights on the tower's collapse pattern in an earthquake are investigated. The study results show that explicit dynamic analysis can be easily applied to member fractures and that this method is suitable for calculating the seismic collapse of a power transmission tower. The selection of the member element failure rule has a significant impact on the forecast collapse pattern of a power transmission tower in an earthquake. The compression member buckling and softening failure rule, coupling the material nonlinearity with elastic buckling phenomenon, can stave off the effort in modeling the constructional eccentricities, which result in Euler buckling. For different earthquake waves, the high-rise power transmission tower demonstrates different collapse failure modes. The static collapse pattern from a pushover analysis and the dynamic collapse pattern are very different. The actual collapse pattern of a power transmission tower during the Wenchuan earthquake and the computer simulated collapse pattern are compared to validate the algorithm proposed in this paper. Finally, the seismic collapse vulnerability of a high-rise power transmission tower is evaluated based on probability estimate method.

Numerical studies on the effect of plan irregularities in the progressive collapse of steel structures

This research examines the effect of plan irregularities on the progressive collapse of four steel structures located in regions with different seismic activity. The plans of the first and second structure are irregular, whilst those of the third and fourth structures are regular. The collapse patterns of the four buildings are examined and compared under seven loading scenarios using non-linear dynamic and static analyses. In the non-linear dynamic analyses, node displacements above the removed columns and the additional force on the columns adjacent to them are discussed. Furthermore, the strength and capacities of the columns are compared to determine their susceptibility to collapse. In the non-linear static analyses, the pushdown curve and yield load factor of the structures are obtained after column removal. The results indicate that an irregular structure designed in site class C seismic zone, collapses in most of the column-removal scenarios. Moreover, when comparing regular and irregular structures designed in site class E seismic zone, the demand force to capacity ratio (D/C) of the columns in the irregular structures is on average between 1.5 and 2 times that of the regular ones.

The importance of drug-induced sedation endoscopy (D.I.S.E.) techniques in surgical decision making: conventional versus target controlled infusion techniques-a prospective randomized controlled study and a retrospective surgical outcomes analysis.

Drug-Induced Sedation Endoscopy (DISE) consists of the direct observation of the upper airways during sedative-induced sleep, allowing the identification of the sites of pharyngeal collapse, which is the main pathological event in Obstructive Sleep Apnea (OSA). The Authors have compared Target Controlled Infusion (TCI) sedation endoscopy (TCI-DISE) technique to conventional DISE (CDISE), performed by a manual bolus injection of sedative agent, to recreate accurately and safely snoring and apnea patterns comparable to natural sleep. The authors conducted a prospective, randomized, long-term study and a retrospective analysis of surgical outcomes. The apnea-event observation and its correlation with pharyngeal collapse patterns is the primary endpoint; secondary endpoints are defined as stability and safety of sedation plan of DISE-TCI technique. From January 2009 to January 2011, OSA patients were included in the study and randomly allocated into two groups: the bolus injection conventional DISE group and the TCI-DISE group. Third endpoint is to compare the surgical outcomes enrolling OSA patients from January 2009 to June 2015. We recorded the complete apnea-event at oropharynx and hypopharynx levels in 15/50 pts in conventional DISE group (30%) and in 99/123 pts in TCI-DISE group (81%) (p < 0.0001). Four pts needed oxygen in conventional DISE group because a severe desaturation occurred during the first bolus of propofol (1mg/kg) (p = 0.4872ns). We recorded instability of the sedation plan in 13 patients of conventional DISE group (65%) and 1 patient of the TCI-DISE group (5%) (p = 0.0001). In 37 TCI-DISE group surgical patients we reported a significant reduction of postoperative AHI (from 42.7 ± 20.2 to 11.4 ± 10.3) in comparison with postoperative AHI in 15C-DISE group surgical patients (from 41.3 ± 23.4 to 20.4 ± 15.5) (p = 0.05). Our results suggest the DISE-TCI technique as first choice in performing sleep-endoscopy because of its increased accuracy, stability and safety. However, it is mandatory an accurate assessment of PSG/PM, which allows us to differentiate OSA patients in whom UA anatomical abnormalities are predominant in comparison with not-anatomical pathophysiologic factors, achieving good surgical patient's selection and outcomes as a consequence.

The Behavior Semi-precast Slab Under Dynamic Load

Driven by increase in trend of construction two storey house in the community, more bamboo and wood are needed to construct formwork in the traditional concreting method. The present of waste from the discarded wooden formwork make the construction method is an inefficient and environmentally unfriendly. A semi-precast method offers a more economical method of construction owing to its less use of bamboo/wood in slab concreting process. This study is intended to characterize the dynamic behavior of semi-precast slab. There were 5 full scale slab specimens cast for this research. One specimen was monolith slab that acts as a control specimen. While the other 4 specimens were made with various shear connector arrangements. On each slab specimens, the dynamic testing was firstly proceeded. The dynamic testing was conducted to determine the dynamic characteristics, displacement mode, mode curvature and absolute difference of curvature mode of slab. The static test was carried out when the dynamic was completed to determine the ultimate capacity as well as collapse pattern of slab being tested. The results showed that there were differences in natural frequency for each slabs, either monolithic or semi-precast slabs. Monolith slab has natural frequency of 14.84Hz, while semi-precast slab without shear connector has natural frequency of 13.45Hz. Semi-precast slab with shear connector spacing of L/4(100) - L/2(150) - L/4(100), L/3(100) - L/3(150) - L/3(100) and 100mm have natural frequency of 13.62Hz, 13.46Hz and 15.97Hz. Displacement mode of monolith slab is smaller than that of semi-precast slab. These test results show that semi-precast slab has a slightly lower stiffness than monolith slab, but it has the same strength characteristics. An indication of similarity was also found between the characteristic of absolute difference of curvature mode and the crack pattern occur in slab that suggest the potential use of absolute difference of curvature mode to predict crack pattern in concrete structural members. In general, the results showed that semi-precast slab has similar structural characteristics to monolithic plates.

Charcot Collapse: Does Collapse Pattern Dictate Osseous Metabolism?

Level III.

Kajian Kuat Tekan Material Tanah Lempung dan Pasir Berbahan Campur Sampah Plastik Rumah Tangga

In Indonesia, the waste has become a national issue which must be managed in a comprehensive and integrated from upstream to downstream in order to provide economic benefits, healthy for the community, and safe for the environment, and can change people's behavior. From various types of waste, plastic is a very dangerous household waste. One effort to reduce dam use plastic waste is to be made as mixing clay and sand to produce material that can be used as building materials. In this research molten plastic waste was mixed with clay and sand with variations of ratio plastic-sand and plastic-clay is 1: 2, 1: 3 and 1: 4. The results revealed that the optimum ratio of plastic-sand mixture is 1: 3 with a compressive strength of 13.5 MPa and the optimum mix of plastic-clay is 1: 2 with a compressive strength of 14.21 MPa. The collapse pattern that occurred in the plastic-sand mixture was shear failure that caused test object splitting, while the plastic-clay mixture is shear failure, but without causing the test object splitting.

Hypoglossal nerve stimulation for obstructive sleep apnea: A review of the literature.

ObjectiveTo review the indications and clinical evidence supporting hypoglossal nerve stimulation (HNS) therapy for the treatment of moderate-to-severe obstructive sleep apnea (OSA).MethodsPeer reviewed literature on hypoglossal nerve stimulation therapy for obstructive sleep apnea from 2001 to 2016.ResultsThe only currently FDA-approved HNS device for the treatment of moderate-to-severe OSA is produced by Inspire Medical Systems, which recently published its 36-month outcomes data from its Stimulation Therapy for Apnea Reduction (STAR) trial. HNS therapy is currently indicated for moderate-to-severe OSA patients who are CPAP-intolerant, have a body mass index <32, apnea-hypopnea index <50, and without a concentric pattern of upper airway collapse on sleep endoscopy.ConclusionsData from the STAR trial suggests that a subset of OSA patients can achieve a significant therapeutic response from hypoglossal nerve stimulation. However, these results may be limited in their generalizability to the broader OSA population.

Vectorial effect of hybrid polarization states on the collapse dynamics of a structured optical field.

The collapse dynamics of a structured optical field with a distribution of spatially-variant states of polarization (SoP) and a spiral phase in the field cross section is studied using the two-dimensional coupled nonlinear Schrӧdinger equations. The self-focusing of a structured optical field with an inhomogeneous SoP distribution can give rise to new phenomena of collapse dynamics that is completely different from a scalar field. The collapse patterns are closely related to the topological charges of the vortexas well as the polarization, the initial power, and the SoP distribution in the field cross section. A single on-axis collapse or multiple off-axis partial collapses may occur due to the self-focusing effects of linearly, elliptically and circularly polarized components located at different positions of the field cross-section. The polarization in the core of the collapsing beam is always linearly polarized. The structured collapsing beams, which are driven by the vortex, propagate along a spiral trajectory in a saturated medium.

Assessment of disproportionate collapse behavior of cable stayed bridges

Although the application of the Alternate Path method has well proven its efficiency towards increasing the structural robustness of bare frame structures against progressive collapse, it should be further developed for bridge structures, and especially cable stayed bridges, as they are the only ty pe routinely designed for cable loss phenomenon. The main objective of this paper is to analyse a cable stayed bridge for multiple types of cable loss phenomenon to develop a profound knowledge regarding the overall structural response to local failure and the possibility of a failure progression throughout the structure. This paper demonstrates numerical modelling and analysis of a typical cable stayed bridge through a nonlinear static procedure using SAP 2000. The response of the structural model is discussed for multiple types of cable loss cases to identify a definite progressive collapse pattern. Furthermore, a categorical investigation of the impact ratios was also done for different structural properties through a dynamic analysis to recognize the lack of robustness in the structure. The results indicate different design considerations for different elements of the structure and also a variation in the possibility of failure progression through the cable stayed model depending upon the location of the failed cables. The prevailing collapse type is discussed with some suggestions for a more robust design.